[PowerPC] enable optimizeCompareInstr for branch with static branch hint

In optimizeCompareInstr, a compare instruction is eliminated by using a record form instruction if possible.
If the branch instruction that uses the result of the compare has a static branch hint, the optimization does not happen.
This patch makes this optimization happen regardless of the branch hint by splitting branch hint and branch condition before checking the predicate to identify the possible optimizations.

Differential Revision: https://reviews.llvm.org/D35801

llvm-svn: 309255