For FreeBSD on mips, pass -G options to the linker

Summary:
On {mips,mipsel,mips64,mips64el}-freebsd, we need to pass any -G option to the linker.  See also:

https://gcc.gnu.org/onlinedocs/gcc/MIPS-Options.html#index-G-2007

This has been adapted from https://reviews.freebsd.org/D1190, with an added test case.

Reviewers: theraven, atanasyan, emaste

Subscribers: brooks, tomatabacu, cfe-commits, seanbruno, emaste

Differential Revision: http://reviews.llvm.org/D9114

llvm-svn: 256461