[VE] Support br_cc comparing fp128

Support br_cc instruction comparing fp128 values.  Add a br_cc.ll
regression test for all kind of br_cc instructions.  And, clean
existing branch regression tests, this time.  Clean a brcond.ll
regression test for brcond instruction.  Remove mixed branch1.ll
regression test.

Reviewed By: simoll

Differential Revision: https://reviews.llvm.org/D89627