[Bug jit/85384] libgccjit does not work if --with-gcc-major-version is used

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85384

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Richard prefered David's patch and we have some sed invocations that expect
s/something.*// to match everything until end of line in gcc/Makefile.in, so if
some sed versions don't do it, it would break other things.

So, fixed for GCC8+ so far, should be backported to 7 at some point.