[clang] [memprof] Export __memprof_default_options_str on Darwin (PR #128920)

[Teresa Johnson via cfe-commits]

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@@ -1617,6 +1617,10 @@ void DarwinClang::AddLinkRuntimeLibArgs(const ArgList &Args,
     }
   }
 
+  if (Sanitize.needsMemProfRt())
+    if (hasExportSymbolDirective(Args))
+      addExportedSymbol(CmdArgs, "___memprof_default_options_str");
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teresajohnson wrote:

Can you add a comment about the added `_` prefix? Also, I think it would be nice to just move the name to ProfileData/MemProf.h. If I look at the ProfileData/InstrProf.h included here for example, it contains helper functions to get runtime function names, so this would seem like a good equivalent place for memprof.

https://github.com/llvm/llvm-project/pull/128920