[clang][Diagnostics] Make 'note' color CYAN (#66997)

Just using BLACK makes it invisible in terminals with a dark background.

Author: tbaederr

clang/docs/ReleaseNotes.rst

@@ -212,6 +212,8 @@ Improvements to Clang's diagnostics
   (`#51567: <https://github.com/llvm/llvm-project/issues/51567>`_)
 - Clang now diagnoses narrowing implicit conversions on variable initializers in immediate
   function context and on constexpr variable template initializers.
+- Clang now prints its 'note' diagnostic in cyan instead of black, to be more compatible
+  with terminals with dark background colors. This is also more consistent with GCC.
 
 Bug Fixes in This Version
 -------------------------

clang/lib/Frontend/TextDiagnostic.cpp

@@ -24,8 +24,7 @@
 
 using namespace clang;
 
-static const enum raw_ostream::Colors noteColor =
-  raw_ostream::BLACK;
+static const enum raw_ostream::Colors noteColor = raw_ostream::CYAN;
 static const enum raw_ostream::Colors remarkColor =
   raw_ostream::BLUE;
 static const enum raw_ostream::Colors fixitColor =