Fix s390x regressions (#3330)

- Add relocation handling needed after PR #3275
- Fix incorrect handling of signed constants detected by PR #3056 test
- Fix LabelUse max pos/neg ranges; fix overflow in buffers.rs
- Disable fuzzing tests that require pre-built v8 binaries
- Disable cranelift test that depends on i128
- Temporarily disable memory64 tests

build.rs

@@ -201,6 +201,8 @@ fn ignore(testsuite: &str, testname: &str, strategy: &str) -> bool {
             ("reference_types", _) if cfg!(feature = "old-x86-backend") => return true,
             // No simd support yet for s390x.
             ("simd", _) if platform_is_s390x() => return true,
+            // No memory64 support yet for s390x.
+            ("memory64", _) if platform_is_s390x() => return true,
             _ => {}
         },
         _ => panic!("unrecognized strategy"),