define NDEBUG in MSVC/nmake release builds

Some headers, like assert.h, check for the presence of NDEBUG.
We already define NDEBUG for MSVC/vcproj release builds.

Task-number: QTBUG-3389

Change-Id: I3b1510d47ff80611aa8072e66492ff2d648393eb
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
(cherry picked from commit ebc4fb452ac268657023cb957c1b0ca0e315b9fc)
unmess CONFIG/QT_CONFIG static/shared

bring it to the state of 5.0.2: both QT_CONFIG and CONFIG in qconfig.pri
contain the respective flag, so it is a) visible how qt was built and b)
user code has a consistent default.

before, on windows we had it only in qconfig.pri's CONFIG (so it was
harder to find the qt config), and on unix we had it only in
.qmake.cache's CONFIG (so it was impossible to find the qt config in a
clean way, and there was no default (other than some arbitrary mess
inside qmake itself)).

Change-Id: Iad06de8c4435cec3e1407babde037ac96cb5bf66
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>