qt: fix webkit/sqlite build without largefile support

The embedded sqlite module forces FILE_OFFSET_BITS=64 unless
SQLITE_DISABLE_LFS is defined, breaking the build for !largefile toolchains.
Webkit internally builds sqlite, so that's affected as well.

Fix it by passing -DSQLITE_DISABLE_LFS in C/CXXFLAGS for !largefile
builds, similar to how we do it for the standalone sqlite package.

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