[lld] [lld][MachO] Prevent doubled N_SO when comp_dir and name absolute (PR #71608)

[Daniel Thornburgh via llvm-commits]

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@@ -1522,13 +1522,17 @@ void ObjFile::registerEhFrames(Section &ehFrameSection) {
 }
 
 std::string ObjFile::sourceFile() const {
+  const char *unitName = compileUnit->getUnitDIE().getShortName();
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mysterymath wrote:

Seems more robust just to use the same comment as there.

https://github.com/llvm/llvm-project/pull/71608