Generate moc and rcc files in the gyp build directory

The real problem that this patch fixes is that moc and rcc generated
files are added to the gyp sources variable with an absolute path,
which for some reason triggers gyp to place the output file in the
same directory as the source instead of the Release or Debug
directories. This causes the last compiled file to be shared by both
the release and debug builds when building debug-and-release, and
MSVC will fail linking if the linked files have incompatible CRTs.

This patch fixes the issue by moving both the generated cpp files
and their compiled objects under <(SHARED_INTERMEDIATE_DIR), which
points to (Release|Debug)/gen.

Change-Id: I4143340acf56c3c7ed665aaae8f6221c310aafa9
Reviewed-by: Andras Becsi <andras.becsi@digia.com>
Reviewed-by: Michael Bruning <michael.bruning@digia.com>