Problem building mm-common on MSYS2

Hello List.

For the last 2 Days I try to build mm-common-* from the Tarball but it 
always ends with an error.

* OS: Windows 10, 20H2
* Dev Environment: MinGW-w64 on MSYS2, 10.2.0
* Doxygen, Graphviz etc. are installed. But I do not know if anything 
else is missing as there is zero Documentation for building mm-common 
itself. (Unless I misunderstand the Infos in the Git Repo Readme?). I 
checked the Internet and installed the Dependencies listed under 
packages-dot-archlinux-dot-com and installed everything that is listed 
there.

Disclaimer: I try to get the overall Dependencies for Building GTK4 and 
GTKMM4 from Source fulfilled, to fully start using and learning GTK4. I 
am still new to the GNOME Environment itself.

Any help is appreciated.

Thanks in advance!
Oliver

*** meson Options ***
These are the Commands and Options I use:
* meson 
--prefix="${SYSTEMDRIVE}/Dev/Sources/GTK4/mmcommon/x64/debug/"${PWD}/build/ 
.
* meson compile --verbose -C ${PWD}/build/
* meson install -C ${PWD}/build/

*** Full Output ***
The Meson build system
Version: 0.57.2
Source dir: C:/Dev/MMCommonSrc
Build dir: C:/Dev/MMCommonSrc/build
Build type: native build
Project name: mm-common
Project version: 1.0.2
Host machine cpu family: x86_64
Host machine cpu: x86_64
Program python3 found: YES (C:\Dev\msys64\mingw64\bin/python3.EXE)
Configuring mm-common.m4 using configuration
Program aclocal found: YES (sh C:\Dev\msys64\usr\bin/aclocal)
Program C:\Dev\msys64\mingw64\bin/python3.EXE found: YES 
(C:\Dev\msys64\mingw64\bin/python3.EXE)
Configuring mm-common-libstdc++.pc using configuration
Configuring mm-common-util.pc using configuration
Configuring mm-common-libstdc++-uninstalled.pc using configuration
Configuring mm-common-util-uninstalled.pc using configuration
Configuring mm-common-get using configuration
Configuring mm-common-get.1 using configuration
Configuring mm-common-prepare using configuration
Configuring mm-common-prepare.1 using configuration
Message:
------
mm-common 1.0.2

        Use network: false
Directories:
             prefix: C:/Dev/Sources/GTK4/mmcommon/x64/debug
             bindir: C:/Dev/Sources/GTK4/mmcommon/x64/debug/bin
            datadir: C:/Dev/Sources/GTK4/mmcommon/x64/debug/share
             docdir: 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/doc/mm-common
   aclocal_macrodir: C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/aclocal
       pkgconfigdir: C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/pkgconfig
         pkgdatadir: C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/mm-common
   build_supportdir: 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/mm-common/build
         doctooldir: 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/mm-common/doctool
         doctagsdir: 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/mm-common/doctags
            man1dir: C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/man/man1
------
Build targets in project: 2

Found ninja-1.10.2 at C:\Dev\msys64\mingw64\bin/ninja.EXE
ninja: Entering directory `C:/Dev/MMCommonSrc/build'
[1/2] "C:\Dev\msys64\mingw64\bin/python3.EXE" 
"C:/Dev/MMCommonSrc/util/meson_aux/libstdcxx-tag.py" "none" 
"C:/Dev/MMCommonSrc/doctags" "libstdc++.tag"
Warning: libstdc++.tag does not exist.
Copying from the source directory because network is disabled.
If you want an up-to-date copy, reconfigure with the -Duse-network=true 
option.
[2/2] "C:\Dev\msys64\mingw64\bin/python3.EXE" 
"C:/Dev/MMCommonSrc/util/meson_aux/skeletonmm-tarball.py" 
"skeletonmm.tar.xz" "C:/Dev/MMCommonSrc" "skeletonmm/.gitignore" 
"skeletonmm/AUTHORS" "skeletonmm/COPYING" "skeletonmm/ChangeLog" 
"skeletonmm/meson.build" "skeletonmm/meson_options.txt" 
"skeletonmm/README" "skeletonmm/skeletonmm.doap" 
"skeletonmm/doc/reference/Doxyfile.in" 
"skeletonmm/doc/reference/meson.build" "skeletonmm/examples/meson.build" 
"skeletonmm/examples/example1/main.cc" "skeletonmm/skeleton/meson.build" 
"skeletonmm/skeleton/skeletonmm-uninstalled.pc.in" 
"skeletonmm/skeleton/skeletonmm.h" 
"skeletonmm/skeleton/skeletonmm.pc.in" 
"skeletonmm/skeleton/skeletonmmconfig.h.in" 
"skeletonmm/skeleton/skeletonmm/meson.build" 
"skeletonmm/skeleton/skeletonmm/wrap_init.h" 
"skeletonmm/skeleton/src/skeleton.ccg" 
"skeletonmm/skeleton/src/skeleton.defs" 
"skeletonmm/skeleton/src/skeleton.hg" 
"skeletonmm/skeleton/src/skeleton_docs.xml" 
"skeletonmm/skeleton/src/skeleton_enums.defs" 
"skeletonmm/skeleton/src/skeleton_methods.defs" 
"skeletonmm/skeleton/src/skeleton_signals.defs" 
"skeletonmm/skeleton/src/skeleton_vfuncs.defs" 
"skeletonmm/tests/meson.build" "skeletonmm/tests/test1/main.cc" 
"skeletonmm/tests/test2/main.cc" 
"skeletonmm/tools/generate_defs_and_docs.sh" 
"skeletonmm/tools/extra_defs_gen/generate_defs_skeleton.cc" 
"skeletonmm/tools/extra_defs_gen/meson.build" 
"skeletonmm/tools/m4/convert.m4" 
"skeletonmm/tools/m4/convert_skeleton.m4" "skeletonmm/untracked/README"
ninja: Entering directory `C:/Dev/MMCommonSrc/build/'
[1/1] Generating libstdc++.tag with a custom command
Did not check status of libstdc++.tag because network is disabled.
Installing skeletonmm.tar.xz to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/doc/mm-common
Installing libstdc++.tag to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/mm-common/doctags
Installing C:/Dev/MMCommonSrc/am_include/compile-binding.am to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/mm-common/build
Installing C:/Dev/MMCommonSrc/am_include/dist-changelog.am to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/mm-common/build
Installing C:/Dev/MMCommonSrc/am_include/doc-reference.am to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/mm-common/build
Installing C:/Dev/MMCommonSrc/am_include/generate-binding.am to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/mm-common/build
Installing 
C:/Dev/MMCommonSrc/util/build_scripts/check-dllexport-usage.py to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/mm-common/build
Installing C:/Dev/MMCommonSrc/util/build_scripts/dist-build-scripts.py 
to C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/mm-common/build
Installing C:/Dev/MMCommonSrc/util/build_scripts/dist-changelog.py to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/mm-common/build
Installing C:/Dev/MMCommonSrc/util/build_scripts/doc-reference.py to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/mm-common/build
Installing C:/Dev/MMCommonSrc/util/build_scripts/generate-binding.py to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/mm-common/build
Installing C:/Dev/MMCommonSrc/macros/mm-ax_cxx_compile_stdcxx.m4 to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/aclocal
Installing C:/Dev/MMCommonSrc/macros/mm-ax_cxx_compile_stdcxx_11.m4 to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/aclocal
Installing C:/Dev/MMCommonSrc/macros/mm-dietlib.m4 to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/aclocal
Installing C:/Dev/MMCommonSrc/macros/mm-doc.m4 to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/aclocal
Installing C:/Dev/MMCommonSrc/macros/mm-module.m4 to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/aclocal
Installing C:/Dev/MMCommonSrc/macros/mm-pkg.m4 to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/aclocal
Installing C:/Dev/MMCommonSrc/macros/mm-warnings.m4 to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/aclocal
Installing C:/Dev/MMCommonSrc/build/mm-common.m4 to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/aclocal
Installing C:/Dev/MMCommonSrc/util/doc-install.pl to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/mm-common/doctool
Installing C:/Dev/MMCommonSrc/util/doc-postprocess.pl to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/mm-common/doctool
Installing C:/Dev/MMCommonSrc/util/doxygen.css to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/mm-common/doctool
Installing C:/Dev/MMCommonSrc/util/doxygen-extra.css to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/mm-common/doctool
Installing C:/Dev/MMCommonSrc/util/tagfile-to-devhelp2.xsl to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/mm-common/doctool
Installing C:/Dev/MMCommonSrc/build/mm-common-libstdc++.pc to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/pkgconfig
Installing C:/Dev/MMCommonSrc/build/mm-common-util.pc to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/pkgconfig
Installing C:/Dev/MMCommonSrc/build/mm-common-get to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/bin
Installing C:/Dev/MMCommonSrc/build/mm-common-get.1 to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/man/man1
Installing C:/Dev/MMCommonSrc/build/mm-common-prepare to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/bin
Installing C:/Dev/MMCommonSrc/build/mm-common-prepare.1 to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/man/man1
Installing C:/Dev/MMCommonSrc/README to 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/doc/mm-common
Running custom install script 'C:\\Dev\\msys64\\mingw64\\bin/python3.EXE 
C:/Dev/MMCommonSrc/util/meson_aux/extra-install-cmd.py 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/aclocal'
--- stdout ---

--- stderr ---
Traceback (most recent call last):

   File "C:/Dev/MMCommonSrc/util/meson_aux/extra-install-cmd.py", line 
17, in <module>

     result = subprocess.run(['aclocal', '--print-ac-dir'],

   File "C:/Dev/msys64/mingw64/lib/python3.8/subprocess.py", line 493, 
in run

     with Popen(*popenargs, **kwargs) as process:

   File "C:/Dev/msys64/mingw64/lib/python3.8/subprocess.py", line 858, 
in __init__

     self._execute_child(args, executable, preexec_fn, close_fds,

   File "C:/Dev/msys64/mingw64/lib/python3.8/subprocess.py", line 1311, 
in _execute_child

     hp, ht, pid, tid = _winapi.CreateProcess(executable, args,

FileNotFoundError: [WinError 2] The system cannot find the file specified

FAILED: install script 'C:\Dev\msys64\mingw64\bin/python3.EXE 
C:/Dev/MMCommonSrc/util/meson_aux/extra-install-cmd.py 
C:/Dev/Sources/GTK4/mmcommon/x64/debug/share/aclocal' exit code 1, stopped
--- stderr ---