This block provoked a warning on mingw-w64 because we were redefining
_inline. According to Ralf's research, it was introduced in 452ff68a:
Windows 2000 doesn't have getaddrinfo and related functions in
ws2tcpip.h, but does have a shim implementation in wspiapi.h.

At the time of 452ff68a, mingw32 didn't have wspiapi.h, so it's unclear
why there was a __GNUC__ code path here. The "#define _inline" on that
code path looks likely to be some sort of workaround for a faulty version
of wspiapi.h? Current mingw-w64 does have wspiapi.h, so we enter the
__GNUC__ code path and get the redefinition.

dbus no longer supports Windows 2000, so we no longer need wspiapi.h
at all, and can rely on XP or later. (Ralf's policy is to only support
versions of Windows that are still supported by Microsoft, and Windows 2000
reached the end of its life-cycle in 2010.)

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=68852
Reviewed-by: Ralf Habacker