Fixing compiler warning on gcc 4.6.1.

BUG=v8:1831

Review URL: http://codereview.chromium.org/8597006

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10026 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/objects-inl.h

@@ -2298,7 +2298,7 @@ void ConsString::set_second(String* value, WriteBarrierMode mode) {
 
 
 void ExternalString::clear_data_cache() {
-  WRITE_INTPTR_FIELD(this, kResourceDataOffset, NULL);
+  WRITE_INTPTR_FIELD(this, kResourceDataOffset, 0);
 }