Clang: Fix highlighting of primitive types

libClang categorizes these as keywords, so we need to check
if a keyword is actually a primitive type, and use that.

Task-number: QTCREATORBUG-17867
Change-Id: I354bb0422505ed7732a0799d9c86d3acfdeb0785
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

src/libs/clangbackendipc/clangbackendipc_global.h

@@ -74,6 +74,7 @@ enum class HighlightingType : quint8
     Function,
     VirtualFunction,
     Type,
+    PrimitiveType,
     LocalVariable,
     Field,
     GlobalVariable,