configure.ac: remove -fcolor-diagnostics from LLVM flags

When LLVM is build with Clang, "llvm-config --cxxflags" contains the
-fcolor-diagnostics flag. It is not recognized by gcc and the build
fails. Fix by removing the flag.

Signed-off-by: Markus Trippelsdorf <markus@trippelsdorf.de>
Signed-off-by: Brian Paul <brianp@vmware.com>

configure.ac

@@ -1546,6 +1546,7 @@ strip_unwanted_llvm_flags() {
 	-e 's/-O.\>//g' \
 	-e 's/-g\>//g' \
 	-e 's/-Wall\>//g' \
+	-e 's/-fcolor-diagnostics\>//g' \
 	-e 's/-fomit-frame-pointer\>//g'
 }