Use ErrorOS for log messages as well as error

[sbc100]

Summary

These log messages are also diagnostics so it seems like
they should to the same place as errors and debug
messages.

Without this change when I enable --verbose those messages
go to stdout, but when I enable "-mllvm -debug" those messages
go to stderr (because dbgs() goes to stderr by default).

So I end up having to do this a lot:
lld <args> > output_message 2>&1

[sbc100]

• cleanup

[ruiu]

I agree that log should go to stderr, but I think message should still go to stdout. We have that function to print out a regular message, such as printing out version information or some hint message. We have this function mainly because we want to acquire the global lock before printing out something in the multithreaded environment.

[sbc100]

• feedback

[ruiu]

LGTM

[sbc100]

• update tests

Common/ErrorHandler.cpp

 #if !defined(_MSC_VER) && !defined(__MINGW32__)
 #include <unistd.h>
 #endif
 
 using namespace llvm;
 using namespace lld;
 
 // The functions defined in this file can be called from multiple threads,
-// but outs() or errs() are not thread-safe. We protect them using a mutex.
+// but errs() is not thread-safe. We protect them using a mutex.
 static std::mutex Mu;
 
 // Prints "\n" or does nothing, depending on Msg contents of
 // the previous call of this function.
 static void newline(raw_ostream *ErrorOS, const Twine &Msg) {
   // True if the previous error message contained "\n".
   // We want to separate multi-line error messages with a newline.
   static bool Flag;
void lld::exitLld(int Val) {
   // Delete the output buffer so that any tempory file is deleted.
   errorHandler().OutputBuffer.reset();
 
   // Dealloc/destroy ManagedStatic variables before calling
   // _exit(). In a non-LTO build, this is a nop. In an LTO
   // build allows us to get the output of -time-passes.
   llvm_shutdown();
 
-  outs().flush();
   errs().flush();
   _exit(Val);
 }
 
 void ErrorHandler::print(StringRef S, raw_ostream::Colors C) {
   *ErrorOS << LogName << ": ";
   if (ColorDiagnostics) {
     ErrorOS->changeColor(C, true);
     *ErrorOS << S;
     ErrorOS->resetColor();
   } else {
     *ErrorOS << S;
   }
 }
 
 void ErrorHandler::log(const Twine &Msg) {
   if (Verbose) {
     std::lock_guard<std::mutex> Lock(Mu);
-    outs() << LogName << ": " << Msg << "\n";
-    outs().flush();
+    *ErrorOS << LogName << ": " << Msg << "\n";
   }
 }
 
 void ErrorHandler::message(const Twine &Msg) {
   std::lock_guard<std::mutex> Lock(Mu);
-  outs() << Msg << "\n";
-  outs().flush();
+  *ErrorOS << Msg << "\n";
 }
 
 void ErrorHandler::warn(const Twine &Msg) {
   if (FatalWarnings) {
     error(Msg);
     return;
   }