'with-docs' fails in gcc based MSYS2 shells

For some mysterious reason, it's impossible to generate introspected docs in UCRT64 and MINGW32. The docs can be generated fine in CLANG* shells.

[126/204] Generating docs/index.html.tmp with a custom command (wrapped by meson to set PATH, to capture output)
FAILED: docs/index.html.tmp 
"C:/msys64/mingw32/bin/meson" "--internal" "exe" "--unpickle" "C:/_r/_builds/vJWzEqDv/0/GNOME/gimp/_babl/_build-x86/meson-private/meson_exe_env.EXE_71725d30da667b6bc1fc1c3b1c18c4e22e54b2a0.dat"