Removing _LIBCPP_DISABLE_UNUSED_STRUCT_WARNINGS from libc++ enables

`[[gnu::__warn_unused__]]` on standard library types (such as
`std::string` and `std::set`), surfacing `-Wunused-variable` warnings
in `//third_party/flatbuffers`. See [upstream LLVM commit](https://github.com/llvm/llvm-project/commit/ab8b037ef7b398aa864959a69f328fa69b567f74) for reference.

Remove unreferenced variable declarations across the code generators and
binary annotator whose initializers have no observable side effects.

PiperOrigin-RevId: 999136370

rust/flatbuffers/src/push.rs

@@ -83,11 +83,6 @@ macro_rules! impl_push_for_endian_scalar {
             unsafe fn push(&self, dst: &mut [u8], _written_len: usize) {
                 emplace_scalar::<$ty>(dst, *self);
             }
-
-            #[inline]
-            fn alignment() -> PushAlignment {
-                PushAlignment::new(size_of::<$ty>())
-            }
         }
     };
 }
@@ -103,23 +98,3 @@ impl_push_for_endian_scalar!(u64);
 impl_push_for_endian_scalar!(i64);
 impl_push_for_endian_scalar!(f32);
 impl_push_for_endian_scalar!(f64);
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    #[test]
-    fn endian_scalar_push_alignment_matches_wire_size() {
-        assert_eq!(<bool as Push>::alignment().value(), 1);
-        assert_eq!(<u8 as Push>::alignment().value(), 1);
-        assert_eq!(<i8 as Push>::alignment().value(), 1);
-        assert_eq!(<u16 as Push>::alignment().value(), 2);
-        assert_eq!(<i16 as Push>::alignment().value(), 2);
-        assert_eq!(<u32 as Push>::alignment().value(), 4);
-        assert_eq!(<i32 as Push>::alignment().value(), 4);
-        assert_eq!(<f32 as Push>::alignment().value(), 4);
-        assert_eq!(<u64 as Push>::alignment().value(), 8);
-        assert_eq!(<i64 as Push>::alignment().value(), 8);
-        assert_eq!(<f64 as Push>::alignment().value(), 8);
-    }
-}

src/idl_gen_java.cpp

@@ -2176,6 +2176,7 @@ class JavaGenerator : public BaseGenerator {
       if (field.deprecated) continue;
       if (field.value.type.base_type == BASE_TYPE_UTYPE) continue;
       if (field.value.type.element == BASE_TYPE_UTYPE) continue;
+      const auto get_field = namer_.Method("get", field);
 
       code += "    this." + namer_.Field(field) + " = ";
       const auto type_name =

src/idl_gen_swift.cpp

@@ -1141,6 +1141,7 @@ class SwiftGenerator : public BaseGenerator {
          it != struct_def.fields.vec.end(); ++it) {
       const auto& field = **it;
       if (field.deprecated) continue;
+      const auto offset = NumToString(field.value.offset);
 
       code_.SetValue("FIELDVAR", namer_.Variable(field));
       code_.SetValue("VALUETYPE", GenerateVerifierType(field));