Hi, 
I propose the following patch series for current guile 3 development.
With these patches applied, on i686 and x86_64 I got until

  CCLD     guile.exe
  GEN      guile-procedures.texi
Backtrace:
           0 (primitive-load-path "C:/Users/hm/Documents/msys32/…")

ERROR: In procedure primitive-load-path:
In procedure primitive-load-path: Unable to find file
"C:/Users/hm/Documents/msys32/home/hm/mingw-w64-guile-2.9.2/src/build-
i686-w64-mingw32/libguile/C:/Users/hm/Documents/msys32/home/hm/mingw-
w64-guile-2.9.2/src/build-i686-w64-mingw32/meta/guild" in load path
make[3]: *** [Makefile:4295: guile-procedures.texi] Error 1

The latest error is related to building absolute path names, which
seems not new but I do not know how to fix it.

But I was able on i686 and x86_64 to run simple guile commands with
relative path names 
GUILE_AUTO_COMPILE=0 ../meta/build-env ./.libs/guile -l
../../../../test.scm

My configuration was:
autoreconf -fi
configure \
    --prefix=${MINGW_PREFIX} \
    --build=${MINGW_CHOST} \
    --host=${MINGW_CHOST} \
    --enable-shared \
    --enable-static \
    --enable-error-on-warning=no \
    --enable-jit=no

Attached also the used draft PKGBUILD file for mingw-w64.

Thanks
Hannes