Make clang tools ignore -fcolor-diagnostics and -fdiagnostics-color retrieved from the compilation database.

Summary:
Clang tools' diagnostic output could be force colored when a command
line from the compilation database contains -fcolor-diagnostics or
-fdiagnostics-color. This is not what we want e.g. for vim integration.

Reviewers: klimek

Reviewed By: klimek

CC: cfe-commits, revane, jordan_rose

Differential Revision: http://llvm-reviews.chandlerc.com/D917