[PowerPC] Use record-form instruction for Less-or-Equal -1 and Greater-or-Equal 1

Currently a record-form instruction is used for comparison of "greater than -1" and "less than 1" by modifying the predicate (e.g. LT 1 into LE 0) in addition to the naive case of comparison against 0.
This patch also enables emitting a record-form instruction for "less than or equal to -1" (i.e. "less than 0") and "greater than or equal to 1" (i.e. "greater than 0") to increase the optimization opportunities.

Differential Revision: https://reviews.llvm.org/D38941

llvm-svn: 316647