[Support] Don't tie errs() to outs() by default

This reverts part of D81156.

Accessing errs() concurrently was safe before and racy after D81156.
(`errs() << 'a'` is always racy)

Accessing outs() and errs() concurrently was safe before and racy after D81156.

Don't tie errs() to outs() by default to fix the fallout.
llvm-dwarfdump is single-threaded and opting in the tie behavior is safe.

Author: MaskRay

llvm/lib/Support/raw_ostream.cpp

@@ -878,7 +878,6 @@ raw_fd_ostream &llvm::outs() {
 raw_fd_ostream &llvm::errs() {
   // Set standard error to be unbuffered and tied to outs() by default.
   static raw_fd_ostream S(STDERR_FILENO, false, true);
-  S.tie(&outs());
   return S;
 }
 

llvm/tools/llvm-dwarfdump/llvm-dwarfdump.cpp

@@ -606,6 +606,10 @@ static std::vector<std::string> expandBundle(const std::string &InputPath) {
 int main(int argc, char **argv) {
   InitLLVM X(argc, argv);
 
+  // Flush outs() when printing to errs(). This avoids interleaving output
+  // between the two.
+  errs().tie(&outs());
+
   llvm::InitializeAllTargetInfos();
   llvm::InitializeAllTargetMCs();