MIPS64R6 compact branch support. As the MIPS LLVM backend uses distinct
MachineInstrs for certain 32 and 64 bit instructions (e.g. BEQ & BEQ64) that
map to the same instruction, extend compact branch support for the
corresponding 64bit branches.
Reviewers: dsanders
Differential Revision: https://reviews.llvm.org/D20164
llvm-svn: 276739
Simon Dardis