CxxUtils: Suppress gcc12 uninitialized value false positive.

gcc12 is more aggressive at warning about uninitialized values.

In the CachedValue move ctor, we move the contained value if m_cacheValue is set to VALID. If we get there, then the value should have been properly initialized. But gcc12 seems to have difficulty in proving this in all cases. So suppress a maybe-uninitialized warning around the move of the value.