[BranchFolding] Set correct mem refs (2nd try)

This is a recommit of r257253 which was reverted in r257270.
Previous testcase can make failure on some targets due to using opt with O3 option.

Original Summary:
Merge MBBICommon and MBBI's MMOs.

Differential Revision: http://reviews.llvm.org/D15990

llvm-svn: 257317