refactor: disable self-assign warning for tests

clang-16 and earlier detect "foo -= foo" and "foo /= foo" as self-assignments.

src/test/fuzz/muhash.cpp

@@ -43,7 +43,19 @@ FUZZ_TARGET(muhash)
         },
         [&] {
             // Test that dividing a MuHash by itself brings it back to it's initial state
+
+            // See note about clang + self-assignment in test/uint256_tests.cpp
+            #if defined(__clang__)
+            #    pragma clang diagnostic push
+            #    pragma clang diagnostic ignored "-Wself-assign-overloaded"
+            #endif
+
             muhash /= muhash;
+
+            #if defined(__clang__)
+            #    pragma clang diagnostic pop
+            #endif
+
             muhash.Finalize(out);
             out2 = uint256S(initial_state_hash);
         },

src/test/uint256_tests.cpp

@@ -267,6 +267,22 @@ BOOST_AUTO_TEST_CASE( conversion )
 
 BOOST_AUTO_TEST_CASE( operator_with_self )
 {
+
+/* Clang 16 and earlier detects v -= v and v /= v as self-assignments
+   to 0 and 1 respectively.
+   See: https://github.com/llvm/llvm-project/issues/42469
+   and the fix in commit c5302325b2a62d77cf13dd16cd5c19141862fed0 .
+
+   This makes some sense for arithmetic classes, but could be considered a bug
+   elsewhere. Disable the warning here so that the code can be tested, but the
+   warning should remain on as there will likely always be a better way to
+   express this.
+*/
+
+#if defined(__clang__)
+#    pragma clang diagnostic push
+#    pragma clang diagnostic ignored "-Wself-assign-overloaded"
+#endif
     arith_uint256 v = UintToArith256(uint256S("02"));
     v *= v;
     BOOST_CHECK(v == UintToArith256(uint256S("04")));
@@ -276,6 +292,9 @@ BOOST_AUTO_TEST_CASE( operator_with_self )
     BOOST_CHECK(v == UintToArith256(uint256S("02")));
     v -= v;
     BOOST_CHECK(v == UintToArith256(uint256S("0")));
+#if defined(__clang__)
+#    pragma clang diagnostic pop
+#endif
 }
 
 BOOST_AUTO_TEST_CASE(parse)