Highlight various parts of the AST dump with color.  Colors are controlled by
-f(no-)color-diagnostics.  In addition, dumpColor() function calls are added
to force color printing.  No structural changes to -ast-dump.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@173548 91177308-0d34-0410-b5e6-96231b3b80d8