[dsymutil] Gather function ranges during DIE selection.

Gather the function ranges [low_pc, high_pc) during DIE selection and
store them along with the offset to apply to them to get the linked
addresses.

This is just the data collection part, it comes with no tests. That
information will be used in multiple followup commits to perform the
relocation of line tables and range sections among other things, and
these commits will add tests.

llvm-svn: 231957