build: pass _WIN32_WINNT=0x0601 when building libevent for Windows
build: pass _WIN32_WINNT=0x0601 when building libevent for Windows

This enables of the use of AI_* definitions in the Windows headers,
specifically AI_ADDRCONFIG, which fixes an issue with libevent and
ipv6 on Windows.

It also aligns with what we define in configure when building Core.


Former-commit-id: 3840427ce4e213b4d654c6379878be0336e3f7ad
syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin