Issues building scipy

I am creating this thread to discuss issues i encounter while trying
to build scipy

Python is a 3.5.2 built from sources
Numpy is 1.16.4 built from sources. With MKL 2019 link
Scipy is 1.3.0
gfortran is the MINGW64 version 8.1
C compiler is VS2015

First tried platform is win64 / VS2015

First issue i encountered was that gfortran was in a path with spaces,
leading to incorrect command lines because the path to gfortran is not
quoted. I did junbctions to get a path to the same place without
spaces.
I still see some paths with spaces  inb /LIBPATH: arguments of cl, but
strangely that does not seem to bring issues.

Next issue seems to be about undefined symbol _dgtsv. Which seems to
be a lapack symbol. scipy seems to have found site.cfg of numpy build
with mkl config, but the gfortran command line that fails does not
have link to mkl libs references in site.cfg.
Am i right to think i need to pass extra link flags to mkl to
gfortran? How can i do this from setup.py command line or modification
of numpy's site.cfg?

An other strange thing i see is that prior to launching my build
script, i am in a console with environment to find x64 verion of
VS2015 build tools. However, the cl command lines use the x86 version
of the compiler to cross compile for x64
(...\VC\BIN\x86_amd64\cl.exe). Where does that come from? Numpy
distutils?