* gnu/packages/patches/gcc-4.9.3-mingw-gthr-default.patch, gnu/packages/patches/mingw-w64-5.0rc2-gcc-4.9.3.patch, gnu/packages/mingw.scm: New files. * gnu/local.mk (dist_patch_DATA): Add the patches. (GNU_SYSTEM_MODULES): Add mingw.scm.