C++: use CppModelManagerInterface::setExtraDiagnostics.

So removed duplicate code.

Change-Id: Ibee9964dce032215c8ef556e7143783285294874
Reviewed-by: Sergey Shambir <sergey.shambir.auto@gmail.com>
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>
Clang: suppress uninformative PCH generation messages.

When not using PCH files, suppress the message when successfully
switching to that mode instead of 'Successfully generated PCH file ""'.

Change-Id: Id01af83072c4c65116f15f7edf9079b4b0298182
Reviewed-by: Sergey Shambir <sergey.shambir.auto@gmail.com>
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>
Clang: turn off clang indexing.

It's not ready for prime-time yet.

Change-Id: I1000b82fe6a85c5d45147dc721d8afe52705d865
Reviewed-by: Sergey Shambir <sergey.shambir.auto@gmail.com>
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>
Clang: tune injected defines to suppress warnings.

Change-Id: I9c4a295f3a53d26f51a26121514587f0abc407e1
Reviewed-by: Sergey Shambir <sergey.shambir.auto@gmail.com>
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>
Clang: 3.3 is coming, so assume that is used on Mac.

Change-Id: I76fec22c4a69e17ffe002f2c835e68f7993c77ce
Reviewed-by: Sergey Shambir <sergey.shambir.auto@gmail.com>
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>