autotools: move checking for zmq library to common area in configure.ac

[jmcorgan]

Fixes #6679

[jmcorgan]

Looks like Windows builds are failing, but probably not due to Windows per se. I suspect the new configure.ac logic is not properly shutting off ENABLE_ZMQ when the library is not found.

[jonasschnelli]

I think you need to keep the else with something similar to AC_DEFINE_UNQUOTED([ENABLE_ZMQ],[0],[Define to 1 to enable ZMQ functions]).
Travis Win32/64 does not have a libzmq installed and therefore should not compile the zmq features.

[jmcorgan]

Ah, missed that, thanks.

[jmcorgan]

That didn't work. Calling @theuni ...

[jmcorgan]

The fix required implementing the logic to test for zmq or not when use_pkgconfig was set to no.

[theuni]

@jmcorgan yep, that was the right fix. Although, the non-pkg-config check isn't testing versions. Can you change the AC_CHECK_LIB to test for something new in v4? If there's not a new symbol to check for, we'll have to resort to a quick compile test.

Edit: If this is to be believed, a check for zmq_ctx_shutdown should do the trick.

[theuni]

Nit: Please move the new check up above the protobuf check, so it's not mixed in with the qt stuff.

[jmcorgan]

Understood about check for a 4.x only function in the non-pkgconfig section, but I'm confused by your request for moving the checks to a different place. Can you be more specific about which lines of code you want to move and to which location?

[theuni]

  if test "x$use_zmq" = "xyes"; then
     AC_CHECK_HEADER([zmq.h],

That whole block Up about 5 lines, so it's before BITCOIN_QT_CHECK...

[jmcorgan]

Done.

[jmcorgan]

@theuni This should all be good to go now.

[theuni]

Looks good, ut ACK