i was trying to build mingw-w64-v2.0.7
when doing a make i got the error about a missing m4 folder.
it was a parameter ("-I m4") to aclocal-1.11 from the build system.
then i went to /mingw/share/libtool/libltdl and created such a subdir.
i further had to create a symlink there using "ln -s ../config" to make the build work.
this is seemingly very close to this bug from the SDL_gfx package: