Always use our getaddrinfo.c on Windows.

Commit a16bac36 let "configure" detect
the system getaddrinfo() when building under 64-bit MinGW-w64.  However,
src/include/port/win32/sys/socket.h assumes all native Windows
configurations use our replacement.  This change placates buildfarm
member jacana until we establish a plan for getaddrinfo() on Windows.