Fix the Windows shared build

R=fschneider@chromium.org

BUG=none
TEST=Windows shared build works when pushed to Chromium

Review URL: http://codereview.chromium.org//6932006

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7776 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/v8dll-main.cc

@@ -25,6 +25,9 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+// The GYP based build ends up defining USING_V8_SHARED when compiling this
+// file.
+#undef USING_V8_SHARED
 #include "../include/v8.h"
 
 #ifdef WIN32