Consider alignment contribution from bitfields (#2680)

Author: nbdd0121

bindgen-tests/tests/expectations/tests/bitfield-32bit-overflow.rs

@@ -7,3 +7,14 @@ struct Struct {
     unsigned char e : 8;
 };
 #pragma pack(pop)
+
+struct Inner {
+    unsigned short a: 16;
+    unsigned short b: 16;
+};
+
+#pragma pack(push, 1)
+struct Outer {
+    struct Inner inner;
+};
+#pragma pop

bindgen-tests/tests/expectations/tests/bitfield-method-same-name.rs

@@ -156,9 +156,7 @@ impl<'a> StructLayoutTracker<'a> {
 
         self.latest_field_layout = Some(layout);
         self.last_field_was_bitfield = true;
-        // NB: We intentionally don't update the max_field_align here, since our
-        // bitfields code doesn't necessarily guarantee it, so we need to
-        // actually generate the dummy alignment.
+        self.max_field_align = cmp::max(self.max_field_align, layout.align);
     }
 
     /// Returns a padding field if necessary for a given new field _before_