use vfork if possible in posix_spawn

[musl] / src / process / posix_spawnattr_setsigmask.c

#include <spawn.h>

int posix_spawnattr_setsigmask(posix_spawnattr_t *restrict attr, const sigset_t *restrict mask)
{
        attr->__mask = *mask;
        return 0;
}