qt: update qmake2 class to export qconfig.pri mkspec

This is necessary when Qt applications want to know variables such as
QT_MAJOR_VERSION, QT_VERSION, QT_MINOR_VERSION, GCC version, etc.

(From OE-Core rev: dcaa40e65d986587fa7c44f4285bbd0883478cc3)

Signed-off-by: Felipe F. Tonello <eu@felipetonello.com>
Signed-off-by: Jonathan Liu <net147@gmail.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/qmake2.bbclass

@@ -6,6 +6,7 @@ inherit qmake_base
 DEPENDS_prepend = "qt4-tools-native "
 
 export QMAKESPEC = "${STAGING_DATADIR}/qt4/mkspecs/${TARGET_OS}-oe-g++"
+export OE_QMAKE_QT_CONFIG = "${STAGING_DATADIR}/qt4/mkspecs/qconfig.pri"
 export OE_QMAKE_UIC = "${STAGING_BINDIR_NATIVE}/uic4"
 export OE_QMAKE_UIC3 = "${STAGING_BINDIR_NATIVE}/uic34"
 export OE_QMAKE_MOC = "${STAGING_BINDIR_NATIVE}/moc4"