build: fix mingw-w64 compilation with CMake

[fanquake]

Set ZMQ_HAVE_IPC OFF for all Windows builds, rather than just WindowsStore builds.

This fixes compiling with mingw-w64, and mirrors the autotools builds system:

libzmq/configure.ac

Lines 145 to 152 in 2a75ef0

	# Disable IPC on unsupported platforms.
	case "${host_os}" in
	*vxworks*|*openvms*|*mingw*)
	;;
	*)
	AC_DEFINE(ZMQ_HAVE_IPC, 1, [Have AF_UNIX sockets for ipc transport])
	;;
	esac

[bluca]

Why? AF_UNIX was added some years ago to Windows

[fanquake]

Why? AF_UNIX was added some years ago to Windows

Is there as reason it's still disabled in the autotools build then?

[bluca]

I don't know if anybody uses autotools on windows, doubt it

[fanquake]

I don't know if anybody uses autotools on windows, doubt it

I don't know what you mean. The Autotools build system here is used extensively for cross-compiling Windows libs on Linux, via mingw-w64.

[bluca]

That may very well be, doesn't change the fact that AF_UNIX is available on windows and it doesn't make sense to disable it

[fanquake]

Sure. So what is your preferred approach for handling mingw-w64 builds via CMake? Note that this is the second of two issues (see #4669). Should we handled this in the build system, in the code? Is mingw-w64 officially unsupported via CMake?

[stephanlachnit]

The actual issue with mingw is actually wrong usage of _MSC_VER, I fixed it in #4678