When providing allocation and deallocation traces,
the ASan compiler-rt runtime already provides call
addresses (`TracePCType::Calls`).
On Darwin, system sanitizers (libsanitizers)
provides return address. It also discards a few
non-user frames at the top of the stack, because
these internal libmalloc/libsanitizers stack
frames do not provide any value when diagnosing
memory errors.
Introduce and add handling for
`TracePCType::ReturnsNoZerothFrame` to cover this
case and enable libsanitizers traces line-level
testing.
rdar://157596927
---
Commit 1 is a mechanical refactoring to introduce
and adopt `TracePCType` enum to replace
`pcs_are_call_addresses` bool. It preserve the
current behavior:
```
pcs_are_call_addresses:
false -> TracePCType::Returns (default)
true -> TracePCType::Calls
```
Best reviewed commit by commit.
484d0408f9