On {mips,mipsel,mips64,mips64el}-freebsd, we need to pass any -G option to the assembler.

Summary:
See also:
https://sourceware.org/binutils/docs/as/MIPS-Options.html#index-g_t_0040code_007b_002dG_007d-option-_0028MIPS_0029-1392

Reviewers: theraven, atanasyan, brooks, emaste

Subscribers: rnk, emaste, cfe-commits, seanbruno, dim

Differential Revision: http://reviews.llvm.org/D10137

llvm-svn: 256468