selftests/seccomp: Use __BYTE_ORDER__

Use the compiler-defined __BYTE_ORDER__ instead of the libc-defined
__BYTE_ORDER for consistency.
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211026010831.748682-6-iii@linux.ibm.com

tools/testing/selftests/seccomp/seccomp_bpf.c

@@ -276,12 +276,12 @@ int seccomp(unsigned int op, unsigned int flags, void *args)
 }
 #endif
 
-#if __BYTE_ORDER == __LITTLE_ENDIAN
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 #define syscall_arg(_n) (offsetof(struct seccomp_data, args[_n]))
-#elif __BYTE_ORDER == __BIG_ENDIAN
+#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
 #define syscall_arg(_n) (offsetof(struct seccomp_data, args[_n]) + sizeof(__u32))
 #else
-#error "wut? Unknown __BYTE_ORDER?!"
+#error "wut? Unknown __BYTE_ORDER__?!"
 #endif
 
 #define SIBLING_EXIT_UNKILLED	0xbadbeef