[gold-plugin] Fix a bunch of build warnings

[mgrang]

Fixed the following warnings:

1. gold-plugin.cpp:452:3: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
  case DS_Warning:
  ^
gold-plugin.cpp:452:3: note: insert 'LLVM_FALLTHROUGH;' to silence this warning


2. gold-plugin.cpp:449:8: warning: variable 'Level' is used uninitialized whenever switch case is taken [-Wsometimes-uninitialized]
  case DS_Error:
       ^~~~~~~~
gold-plugin.cpp:461:11: note: uninitialized use occurs here
  message(Level, "LLVM gold plugin: %s",  ErrStorage.c_str());
          ^~~~~
gold-plugin.cpp:447:3: note: variable 'Level' is declared here
  ld_plugin_level Level;

[tejohnson]

tools/gold/gold-plugin.cpp

449–450

Thanks for the fix. I am not sure in fact why we need this separate call to message, rather than just allowing the code to fall through and use the one below the switch statement. I don't see value in the different style of message, particularly now with ThinLTO (looks like this code is quite old, predating ThinLTO).

Can you just remove the call to message() here and instead set Level = LDPL_FATAL here?

[tejohnson]

Lgtm

tools/gold/gold-plugin.cpp

static void diagnosticHandler(const DiagnosticInfo &DI) {
   std::string ErrStorage;
   {
     raw_string_ostream OS(ErrStorage);
     DiagnosticPrinterRawOStream DP(OS);
     DI.print(DP);
   }
   ld_plugin_level Level;
   switch (DI.getSeverity()) {
   case DS_Error:
-    message(LDPL_FATAL, "LLVM gold plugin has failed to create LTO module: %s",
-            ErrStorage.c_str());
+    Level = LDPL_FATAL;
+    break;
   case DS_Warning:
     Level = LDPL_WARNING;
     break;
   case DS_Note:
   case DS_Remark:
     Level = LDPL_INFO;
     break;
   }