[PATCH] [mips] Add assembler support for '.set mipsX'.

[Daniel Sanders]

LGTM. There is a cleanup that I'd like to be done afterwards though.

At the moment, MipsTargetELFStreamer::emitDirectiveSetMips*() and MipsTargetAsmStreamer::emitDirectiveSetMips*() both call setCanHaveModuleDir(). We should move this call to the base class (MipsTargetStreamer), delete  MipsTargetELFStreamer::emitDirectiveSetMips*() since they no longer do anything and have MipsTargetAsmStreamer::emitDirectiveSetMips*() call the base class implementation after emitting the directive.

http://reviews.llvm.org/D4123