Profiler: Fix MSVC warning about signed integers.

src\qml\jsruntime\qv4profiling_p.h(144) :  warning C4146: unary minus operator applied to unsigned type, result still unsigned

Introduced by ac56e7cda724aa7463ef6ffe5f0e93bd3208cb51 .

Change-Id: Ib77234d663bfafd9d55ae2dd551b0aabd6561d6d
Reviewed-by: Ulf Hermann <ulf.hermann@digia.com>
Enable QSG_RUNTIME_DESCRIPTION by default for debug builds.

This can be quite helpful when doing scene graph debugging
with QSG_RENDERER_DEBUG=dump or using qDebug() on nodes
in general.

Change-Id: I6328d3f2a0fad87161c386bed14408598c986dcb
Reviewed-by: Robin Burchell <robin+qt@viroteck.net>