patch at https://launchpadlibrarian.net/877713484/gcc-mingw-w64_29ubuntu1_29ubuntu2.diff.gz
the libgcc build and various other target builds succeed, but the libgfortran build still fails with:
checking whether the GNU Fortran compiler is working... noconfigure: error: GNU Fortran is not working; please report a bug in http://gcc.gnu.org/bugzilla, attaching /<<P
KGBUILDDIR>>/build/i686-w64-mingw32-posix/i686-w64-mingw32/libgfortran/config.log ... because of an invalid host flag.
