mount should include `<sys/mount.h>`

[kbkpbot]

Related to vlang/v#26343 and https://github.com/vlang/v/actions/runs/20957079840/job/60224272468?pr=26343

In file util-vinix/mount/main.v, it should include a C header file.

#include <sys/mount.h>
fn C.mount(source charptr, target charptr, filesystem charptr, flags u64, data voidptr) int

Or it will cause implicit declaration of function ‘mount’ [-Werror=implicit-function-declaration] error/warning