Reapply 'Add reverseColor to raw_ostream'.

To be used in printing unprintable source in clang diagnostics.
Patch by Seth Cantrell, with a minor fix for mingw by me.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@154805 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Support/raw_ostream.cpp

@@ -633,6 +633,19 @@ raw_ostream &raw_fd_ostream::resetColor() {
   return *this;
 }
 
+raw_ostream &raw_fd_ostream::reverseColor() {
+  if (sys::Process::ColorNeedsFlush())
+    flush();
+  const char *colorcode = sys::Process::OutputReverse();
+  if (colorcode) {
+    size_t len = strlen(colorcode);
+    write(colorcode, len);
+    // don't account colors towards output characters
+    pos -= len;
+  }
+  return *this;
+}
+
 bool raw_fd_ostream::is_displayed() const {
   return sys::Process::FileDescriptorIsDisplayed(FD);
 }