On MinGW _WIN32_WINNT needs to be 0x501 (Windows XP) instead of 0x500 (Windows 2000) for some TCP/IP API's to be present.

MinGW uses stdint.h whereas Visual C++ does not.
Review URL: http://codereview.chromium.org/113576

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1999 ce2b1a6d-e550-0410-aec6-3dcde31c8c00