Set RPATH_FLAGS on Mac too

Without this, QMAKE_RPATHDIR is empty and qt_module.prf's logic to turn
on absolute_library_soname fails, causing some modules to build without
absolute paths (eg. qtjsbackend's QtV8 framework).

Change-Id: If03136ca60a5d8a96a589e2d1034e5884fd6a1ac
Reviewed-by: Michael Brasser <michael.brasser@nokia.com>

configure

@@ -5722,6 +5722,8 @@ fi
 if [ "$PLATFORM_MAC" = "yes" ]; then
     if [ "$CFG_RPATH" = "yes" ]; then
        QMAKE_CONFIG="$QMAKE_CONFIG absolute_library_soname"
+       # set the default rpath to the library installation directory
+       RPATH_FLAGS="\"$QT_INSTALL_LIBS\" $RPATH_FLAGS"
     fi
 elif [ -z "`getXQMakeConf 'QMAKE_(LFLAGS_)?RPATH'`" ]; then
     if [ -n "$RPATH_FLAGS" ]; then