Fixed SCons build of Windows DLL.

The configuration for building the Windows shared library was lost when adding x64 Windows build to the SCons build. This should now be back.
Review URL: http://codereview.chromium.org/197036

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2828 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

SConstruct

@@ -258,6 +258,10 @@ V8_EXTRA_FLAGS = {
     'all': {
       'WARNINGFLAGS': ['/WX', '/wd4355', '/wd4800']
     },
+    'library:shared': {
+      'CPPDEFINES': ['BUILDING_V8_SHARED'],
+      'LIBS': ['winmm', 'ws2_32']
+    },
     'arch:ia32': {
       'WARNINGFLAGS': ['/W3']
     },