Hexagon: Expand br_cc.

It fixes following tests for Hexagon:

CodeGen/Generic/2003-07-29-BadConstSbyte.ll
CodeGen/Generic/2005-10-21-longlonggtu.ll
CodeGen/Generic/2009-04-28-i128-cmp-crash.ll
CodeGen/Generic/MachineBranchProb.ll
CodeGen/Generic/builtin-expect.ll
CodeGen/Generic/pr12507.ll