[mips][ias] Stream macro expansions to output instead of buffering them. NFC.

Summary:
This will allows us to eliminate some magic numbers from the offset operand of
branch instructions in favour of symbols and makes it possible to avoid
double-filling delay slots when clang is given -save-temps.

parseDirectiveCpRestore() is calling isIntegratedAssemblerRequired() for the
moment since correctly pushing the generation of these instructions into the
ELF target streamer is tricky enough to warrant a separate patch.

Reviewers: sdardis, vkalintiris

Subscribers: dsanders, llvm-commits, sdardis

Differential Revision: http://reviews.llvm.org/D19164

llvm-svn: 266602