[dsymutil] Avoid relocating DW_AT_call_pc twice

Summary:
Avoid relocating DW_AT_call_pc, e.g. when a call PC is equal to the
function's low_pc as is the case in the test:

```
__Z5func1v:
0000000100007f94        b       __Z5func2v
```

rdar://62952440

Reviewers: friss, JDevlieghere

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D79536