Automatically define WIN32 for MSVC, since some old Platform SDKs don't

automatically define it, but Winsock2.h requires it.


[SVN r34460]

libs/asio

@@ -1 +1 @@
-Subproject commit 57f293b77ccfd1c6dfbcad8397b6d1ffcbbb5a60
+Subproject commit a0962bfdb5a2dbce8a811e1fc1ff5d99315f895f