bcachefs: Fixes for rust bindgen

bindgen doesn't seem to like u128 or DECLARE_FLEX_ARRAY(), but we can
hack around them.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/mean_and_variance.h

@@ -12,9 +12,12 @@
 /*
  * u128_u: u128 user mode, because not all architectures support a real int128
  * type
+ *
+ * We don't use this version in userspace, because in userspace we link with
+ * Rust and rustc has issues with u128.
  */
 
-#ifdef __SIZEOF_INT128__
+#if defined(__SIZEOF_INT128__) && defined(__KERNEL__)
 
 typedef struct {
 	unsigned __int128 v;

fs/bcachefs/subvolume_types.h

@@ -20,7 +20,11 @@ struct snapshot_t {
 };
 
 struct snapshot_table {
+#ifndef RUST_BINDGEN
 	DECLARE_FLEX_ARRAY(struct snapshot_t, s);
+#else
+	struct snapshot_t	s[0];
+#endif
 };
 
 typedef struct {