[sanitizer][MIPS] Add --target flag for MIPS32

Without the --target flag, clang uses the mips64 triple which selects the n64 abi. We need to add --target=mips-linux-gnu, so that clang can select the correct abi for mips32r2.

Reviewers: dsanders, kcc, samsonov
Subscribers: llvm-commits, mohit.bhakkad, jaydeep
Differential Revision: http://reviews.llvm.org/D9249

llvm-svn: 237675