Revert "Always pass -fcolor-diagnostics to clang."

This commit didn't enable color diagnostics for ninja but confuses jenkins
because it enabled color diagnostics there and now our error scanner cannot
work.

This reverts commit 102fb9de.

cmake/modules/CheckCompiler.cmake

@@ -33,12 +33,10 @@ if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
   string(REGEX REPLACE "^.*[ ]version[ ][0-9]+\\.([0-9]+).*" "\\1" CLANG_MINOR "${_clang_version_info}")
   message(STATUS "Found Clang. Major version ${CLANG_MAJOR}, minor version ${CLANG_MINOR}")
   set(COMPILER_VERSION clang${CLANG_MAJOR}${CLANG_MINOR})
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fcolor-diagnostics")
-  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fcolor-diagnostics")
   if(ccache)
     # https://bugzilla.samba.org/show_bug.cgi?id=8118 and color.
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Qunused-arguments")
-    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Qunused-arguments")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Qunused-arguments -fcolor-diagnostics")
+    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Qunused-arguments -fcolor-diagnostics")
   endif()
 else()
   set(CLANG_MAJOR 0)