bug#73737: configure error at "checking dynamic linker characteristics"

In a build of GNU gettext, with libtool 2.5.3 + Sergey's fix,
on mingw with --disable-shared, I see this error during configuration:

checking whether the x86_64-w64-mingw32-gcc linker (/usr/x86_64-w64-mingw32/bin/ld.exe) supports shared libraries... yes
checking dynamic linker characteristics... ../../gettext-runtime/configure: line 17525: test: yes: unary operator expected
Win32 ld.exe
checking how to hardcode library paths into programs... immediate

At gettext-runtime/configure line 17525 we have this statement:

    # not on $(libdir)/../bin or 32 bits dlls would override 64 bit ones.
    if test yes = $multilib; then                                           <=== HERE
    postinstall_cmds='base_file=`basename \$file`~

Apparently $multilib is empty or expands to more than one word.

This code was added in commit ab89ebbcc2ff0ecff5157982ef03627cfd615f7e .

The main problem is that the variable 'multilib' is never defined in libtool.m4.
Where is it supposed to be defined?

Other than that, this commit has two problems:
  - missing indentation of the two branches of the 'if' statement.
  - a typo (mulitlibs -> multilib)

Bruno