D62056 makes the output color if clang auto-detects a tty, but if it
does not, there is no way to force it to use colors anyway.
My first attempt was to figure out how to plumb the
--use-color command line argument to the DiagnosticEngine
that gets referenced in AST->getDiagnostics().getDiagnosticOptions()
However, this did not turn to be fruitful. Those options get created
in ToolInvocation::run() from the command line given to the *tool*.
That command-line is constructed in ClangTool::run() and there's no
apparent way to edit those Diagnostics from the clang-query tool