[wasm] Fix more -Wsign-compare warnings.

test/cctest/test-run-wasm-relocation-arm64.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <iostream>  // NOLINT(readability/streams)
 
 #include "src/v8.h"
 #include "test/cctest/cctest.h"
 
 #include "src/arm64/simulator-arm64.h"
@@ skipping 34 matching lines @@
   CSignature0<int64_t> csig;
   CodeRunner<int64_t> runnable(isolate, code, &csig);
   int64_t ret_value = runnable.Call();
   CHECK_EQ(ret_value, imm);
 
 #ifdef DEBUG
   OFStream os(stdout);
   code->Print(os);
   ::printf("f() = %" PRIx64 "\n\n", ret_value);
 #endif
-  size_t offset = 1234;
+  int offset = 1234;
 
   // Relocating reference by offset
   int mode_mask = (1 << RelocInfo::WASM_MEMORY_REFERENCE);
   for (RelocIterator it(*code, mode_mask); !it.done(); it.next()) {
     RelocInfo::Mode mode = it.rinfo()->rmode();
     if (RelocInfo::IsWasmMemoryReference(mode)) {
       // Dummy values of size used here as the objective of the test is to
       // verify that the immediate is patched correctly
       it.rinfo()->update_wasm_memory_reference(
           it.rinfo()->wasm_memory_reference(),
@@ skipping 63 matching lines @@
   ret_value = runnable.Call();
   CHECK_NE(ret_value, 0xdeadbeef);
 
 #ifdef DEBUG
   code->Print(os);
   ::printf("f() = %" PRIx64 "\n\n", ret_value);
 #endif
 }
 
 #undef __