Add colored diagnostics when building LLVM with cmake + ninja + clang

When invoked from Ninja, clang does not detect that it can use colors : see ninja-build/ninja#174

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@182878 91177308-0d34-0410-b5e6-96231b3b80d8

cmake/modules/HandleLLVMOptions.cmake

@@ -266,3 +266,10 @@ endif()
 add_llvm_definitions( -D__STDC_CONSTANT_MACROS )
 add_llvm_definitions( -D__STDC_FORMAT_MACROS )
 add_llvm_definitions( -D__STDC_LIMIT_MACROS )
+
+# clang doesn't print colored diagnostics when invoked from Ninja
+if (UNIX AND
+    CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND
+    CMAKE_GENERATOR STREQUAL "Ninja")
+  append("-fcolor-diagnostics" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+endif()