[lld/mac] Extract a reportUndefinedSymbol function

[thakis]

Summary

Makes things look more similar to the ELF port, and removes some
slightly deep nesting.

No behavior change.

[int3]

lgtm

lld/MachO/SymbolTable.cpp

if (!config->deadStripDuplicates || duplicate.sym->isLive()) {
       message += duplicate.src1.second + "\n>>> defined in ";
       if (!duplicate.src2.first.empty())
         message += duplicate.src2.first + "\n>>>            ";
       error(message + duplicate.src2.second);
     }
   }
 }
 
-void macho::reportPendingUndefinedSymbols() {
-  for (const auto &undef : undefs) {
-    const UndefinedDiag &locations = undef.second;
-
-    std::string message = "undefined symbol";
-    if (config->archMultiple)
-      message += (" for arch " + getArchitectureName(config->arch())).str();
-    message += ": " + toString(*undef.first);
+static void reportUndefinedSymbol(const Undefined &sym,
+                                  const UndefinedDiag &locations) {
+  message += ": " + toString(sym);
 
-    const size_t maxUndefinedReferences = 3;
-    size_t i = 0;
-    for (const std::string &loc : locations.otherReferences) {
-      if (i >= maxUndefinedReferences)
-        break;
-      message += "\n>>> referenced by " + loc;
-      ++i;
-    }
 
-    for (const UndefinedDiag::SectionAndOffset &loc :
-         locations.codeReferences) {
-      if (i >= maxUndefinedReferences)
-        break;
-      message += "\n>>> referenced by ";
-      std::string src = loc.isec->getSourceLocation(loc.offset);
-      if (!src.empty())
-        message += src + "\n>>>               ";
-      message += loc.isec->getLocation(loc.offset);
-      ++i;
-    }
+  for (const UndefinedDiag::SectionAndOffset &loc : locations.codeReferences) {
 
-    size_t totalReferences =
-        locations.otherReferences.size() + locations.codeReferences.size();
-    if (totalReferences > i)
-      message +=
-          ("\n>>> referenced " + Twine(totalReferences - i) + " more times")
-              .str();
 
-    if (config->undefinedSymbolTreatment == UndefinedSymbolTreatment::error)
-      error(message);
-    else if (config->undefinedSymbolTreatment ==
-             UndefinedSymbolTreatment::warning)
-      warn(message);
-    else
-      assert(false &&
-             "diagnostics make sense for -undefined error|warning only");
-  }
+    assert(false && "diagnostics make sense for -undefined error|warning only");
 
+void macho::reportPendingUndefinedSymbols() {
+  for (const auto &undef : undefs)
+    reportUndefinedSymbol(*undef.first, undef.second);
+
   // This function is called multiple times during execution. Clear the printed
   // diagnostics to avoid printing the same things again the next time.
   undefs.clear();
 }
 
 void macho::treatUndefinedSymbol(const Undefined &sym, StringRef source) {
   if (recoverFromUndefinedSymbol(sym))
     return;