qt.x86.cflags.diff.gz NOT this makes qt only compiled on x86!!
The SlackBuild I posted (and also the SlackBuild from Slackware 12.2/13.0) does apply this patch only if $ARCH is equal to i486. The only goal of this patch is (was?) to enforce the -march and -mtune defaults of Slackware, but I'm not sure of it being useful anymore since CFLAGS/CXXFLAGS are passed to ./configure in the build script. Anyway, it is pure Slackware policy.