Force ftruncate for shared mem. objects on FreeBSD

FreeBSD does not allow to use posix_fallocate on shared memory objects.

util/shm.c

@@ -42,7 +42,7 @@ int allocate_shm_file(size_t size) {
 		return -1;
 	}
 
-#ifdef WLR_HAS_POSIX_FALLOCATE
+#if defined(WLR_HAS_POSIX_FALLOCATE) && !defined(__FreeBSD__)
 	int ret;
 	do {
 		ret = posix_fallocate(fd, 0, size);