Split getCompileUnitFor{Data,Code}Address.

Getting compile units for data addresses is much slower, as it often
requires a slow fallback path to walk every DWARF entry, as
data addresses don't fall into the compilation unit ranges.

Most lookups are code addresses, and don't need this logic. Split the
functionality out so that we restore the fast-path behaviour for the
code lookups.

More context at:
https://discourse.llvm.org/t/llvm-symbolizer-has-gotten-extremely-slow/67262

Reviewed By: dblaikie

Differential Revision: https://reviews.llvm.org/D145009