[mips] Added support for choosing between traps and breaks in the integrated assembler macros.

Summary: The command line options for these are -Wa,--trap and -Wa,--break.

Patch by Scott Egerton.

Reviewers: vkalintiris, dsanders

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D11676

llvm-svn: 246765