Update llvm-cm against recent LLVM changes

llvm-cm needs to be updated to reflect some recent LLVM changes:
* [ ] BBRanges are now used to represent the basic blocks in a function. `llvm-cm` needs to support these for cases like basic block sections and split machine functions (and should at the very least have test coverage for them).
* [ ] `-mbb-profile-dump` no longer exists, and instead `PGOAnalysisMap` should be used. Tests/code needs to be updated for this.

This (at least the second part) is sort of a prerequisite for #55.