Integrate the BranchRelaxation pass to help with relaxing out-of-range
conditional branches.
This is mostly of concern for SPARCv9, which uses conditional branches with
much smaller range than its v8 counterparts.
(Some large autogenerated code, such as the ones generated by TableGen, already
hits this limitation when building in Release)
Reviewed By: arsenm
Differential Revision: https://reviews.llvm.org/D142458
24e300190a