Fix Win64 build after isolates merge.

Need to add -DWIN32 since the include structure changed.w
Review URL: http://codereview.chromium.org/6712045

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7272 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

SConstruct

@@ -582,7 +582,7 @@ SAMPLE_FLAGS = {
       'LINKFLAGS': ['/MACHINE:X86']
     },
     'arch:x64': {
-      'CPPDEFINES': ['V8_TARGET_ARCH_X64'],
+      'CPPDEFINES': ['V8_TARGET_ARCH_X64', 'WIN32'],
       'LINKFLAGS': ['/MACHINE:X64', '/STACK:2091752']
     },
     'mode:debug': {