Reverted r275257 "[ELF] - Implement extern "c++" version script tag"

It broke build bots:
http://lab.llvm.org:8011/builders/llvm-clang-lld-x86_64-scei-ps4-windows10pro-fast/builds/8204
http://lab.llvm.org:8011/builders/lld-x86_64-freebsd/builds/19432

llvm-svn: 275258
diff --git a/lld/ELF/SymbolListFile.cpp b/lld/ELF/SymbolListFile.cpp
index 1525540..68867cf 100644
--- a/lld/ELF/SymbolListFile.cpp
+++ b/lld/ELF/SymbolListFile.cpp
@@ -77,7 +77,6 @@
   void run();
 
 private:
-  void parseExtern(std::vector<SymbolVersion> *Globals);
   void parseVersion(StringRef Version);
   void parseLocal();
   void parseVersionSymbols(StringRef Version);
@@ -121,38 +120,21 @@
   Config->VersionScriptGlobalByDefault = false;
 }
 
-void VersionScriptParser::parseExtern(std::vector<SymbolVersion> *Globals) {
-  expect("extern");
-  expect("C++");
-  expect("{");
-
-  for (;;) {
-    if (peek() == "}" || Error)
-      break;
-    Globals->push_back({next(), true});
-    expect(";");
-  }
-
-  expect("}");
-  expect(";");
-}
-
 void VersionScriptParser::parseVersionSymbols(StringRef Version) {
-  std::vector<SymbolVersion> *Globals;
+  std::vector<StringRef> *Globals;
   if (Version.empty())
     Globals = &Config->VersionScriptGlobals;
   else
     Globals = &Config->SymbolVersions.back().Globals;
 
   for (;;) {
-    if (peek() == "extern")
-      parseExtern(Globals);
-
     StringRef Cur = peek();
+    if (Cur == "extern")
+      setError("extern keyword is not supported");
     if (Cur == "}" || Cur == "local:" || Error)
       return;
     next();
-    Globals->push_back({Cur, false});
+    Globals->push_back(Cur);
     expect(";");
   }
 }