cplusplus: PPToken - introduce move constructor

profiling qt-creator on my codebase i saw quite a few instances where
reference counting of `QByteArray` showed up in
`Preprocessor::handleFunctionLikeMacro` (hundreds of milliseconds of CPU
time when profiling for a few seconds). using move semantics we can
avoid this source of reference counting.

Change-Id: I19a88a0501064f53d8095f7377bf901e462d25a0
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/libs/cplusplus/PPToken.h

@@ -109,6 +109,10 @@ public:
         : m_src(src)
     {}
 
+    PPToken(QByteArray &&src)
+        : m_src(std::move(src))
+    {}
+
     void setSource(const QByteArray &src)
     { m_src = src; }