file: explicitly disable libseccomp support for host

file: explicitly disable libseccomp support for host

Fixes:
http://autobuild.buildroot.net/results/8a2/8a2ea2e4426416447705492237f526fc84b595d7/
http://autobuild.buildroot.net/results/a1f/a1f2369d31c2387efdec908877e0bcaa728b5aeb/

file-5.33 added optional seccomp support, but the filters did not cover all
needed syscalls, leading to errors when the freshly built host-file is
executed as part of the build on distributions with seccomp support (E.G.
Arch Linux):

checking for seccomp_init in -lseccomp... yes
..
../src/file -C -m magic
make[3]: *** [Makefile:764: magic.mgc] Bad system call

This has been fixed in file-5.34, but it anyway makes sense to explicitly
disable libseccomp support for consistency as we do not need it for the host
build.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>