[driver] Handle the processing of the QA_OVERRIDE_GCC3_OPTIONS and CCC_ADD_ARGS
before the DiagnosticsEngine is instantiated.  Otherwise, warning options are
not handled correctly.
rdar://13254743

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@175779 91177308-0d34-0410-b5e6-96231b3b80d8