[X86] Initialize and Register X86CondBrFoldingPass

To make X86CondBrFoldingPass can be run with --run-pass option, this can test one wrong assertion on analyzeCompare function for SUB32ri when its operand is not imm

Patch by Jianping Chen

Differential Revision: https://reviews.llvm.org/D55412

llvm-svn: 348620