[MinGW] Ignore the sysroot parameter

If the sysroot parameter is passed to the clang frontend, clang
already uses it to find libraries and adds -L options for it, but
also passes it on to the linker. Therefore we can get pretty far
by just ignoring it altogether.

Differential Revision: https://reviews.llvm.org/D37707

llvm-svn: 312945
1 file changed