Add explicit integer type-casts to make WIN64 build without errors.

src/checks.h

Index: src/checks.h
===================================================================
--- src/checks.h	(revision 2791)
+++ src/checks.h	(working copy)
@@ -95,7 +95,39 @@
   }
 }
 
+#ifdef V8_TARGET_ARCH_X64
+// Helper function used by the CHECK_EQ function when given intptr_t
+// arguments.  Should not be called directly.
+static inline void CheckEqualsHelper(const char* file,
+                                     int line,
+                                     const char* expected_source,
+                                     intptr_t expected,
+                                     const char* value_source,
+                                     intptr_t value) {
+  if (expected != value) {
+    V8_Fatal(file, line,
+             "CHECK_EQ(%s, %s) failed\n#   Expected: %i\n#   Found: %i",
+             expected_source, value_source, expected, value);
+  }
+}
 
+
+// Helper function used by the CHECK_NE function when given intptr_t
+// arguments.  Should not be called directly.
+static inline void CheckNonEqualsHelper(const char* file,
+                                        int line,
+                                        const char* unexpected_source,
+                                        intptr_t unexpected,
+                                        const char* value_source,
+                                        intptr_t value) {
+  if (unexpected == value) {
+    V8_Fatal(file, line, "CHECK_NE(%s, %s) failed\n#   Value: %i",
+             unexpected_source, value_source, value);
+  }
+}
+#endif  // V8_TARGET_ARCH_X64
+
+
 // Helper function used by the CHECK function when given string
 // arguments.  Should not be called directly.
 static inline void CheckEqualsHelper(const char* file,