This is a beefed-up version of D33504, which adds support for dwarf 4
debug_frame section format.
The main difference here is that the decision whether to use eh_frame or
debug_frame is done on a per-function basis instead of per-object file.
This is necessary because one module can contain both sections (for
example, the start files added by the linker will typically pull in
eh_frame), but we want to be able to access both, for maximum
I also add unit test for parsing various CFI formats (eh_frame,
debug_frame v3 and debug_frame v4).