qt: update x86x86fix for 32bit pc hosts

The recent change to use config.guess to figure out GNU_HOST_NAME
broken the x86x86fix detection for 32bit hosts, as config.guess
returns something like i686-pc-linux-gnu rather than something with
*-unknown-linux-* like we used to use.

Fix it by simply looking for "linux" instead.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>