[Clang] Move clang::Job::printArg to llvm::sys::printArg. NFCI.

This patch is to support/simplify https://reviews.llvm.org/D80833

include/llvm/Support/Program.h

@@ -210,6 +210,9 @@ namespace sys {
       /// stored.
   );
 
+  /// Print a command argument, and optionally quote it.
+  void printArg(llvm::raw_ostream &OS, StringRef Arg, bool Quote);
+
 #if defined(_WIN32)
   /// Given a list of command line arguments, quote and escape them as necessary
   /// to build a single flat command line appropriate for calling CreateProcess

lib/Support/Program.cpp

@@ -13,6 +13,7 @@
 #include "llvm/Support/Program.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Config/llvm-config.h"
+#include "llvm/Support/raw_ostream.h"
 #include <system_error>
 using namespace llvm;
 using namespace sys;
@@ -75,6 +76,24 @@ bool sys::commandLineFitsWithinSystemLimits(StringRef Program,
   return commandLineFitsWithinSystemLimits(Program, StringRefArgs);
 }
 
+void sys::printArg(raw_ostream &OS, StringRef Arg, bool Quote) {
+  const bool Escape = Arg.find_first_of(" \"\\$") != StringRef::npos;
+
+  if (!Quote && !Escape) {
+    OS << Arg;
+    return;
+  }
+
+  // Quote and escape. This isn't really complete, but good enough.
+  OS << '"';
+  for (const auto c : Arg) {
+    if (c == '"' || c == '\\' || c == '$')
+      OS << '\\';
+    OS << c;
+  }
+  OS << '"';
+}
+
 // Include the platform-specific parts of this class.
 #ifdef LLVM_ON_UNIX
 #include "Unix/Program.inc"