Use .text.unlikely and .text.eh prefixes for MachineBasicBlock sections.
Instead of adding a ".unlikely" or ".eh" suffix for machine basic blocks,
this change updates the behaviour to use an appropriate prefix
instead. This allows lld to group basic block sections together
when -z,keep-text-section-prefix is specified and matches the behaviour
observed in gcc.
Reviewers: tmsriram, mtrofin, efriedma
Reviewed By: tmsriram, efriedma
Subscribers: eli.friedman, hiraditya, llvm-commits
Differential Revision: https://reviews.llvm.org/D78742