libticables: add cmake check for parallel and serial includes

[davide125]

Check for the includes for parallel and serial support and set the relevant defines, so that support can be compiled in when available.

[debrouxl]

The changes look sound. @adriweb ?

[adriweb]

Looks good to me but I'll check on macOS quickly.

[adriweb]

Well, it fails to build now for me:

[ 96%] Linking CXX shared library libticables2.dylib
undef: _cable_par
Undefined symbols for architecture x86_64:
  "_cable_par

We can see the usage here in ticables.cc:

#if !defined(NO_CABLE_PAR) && (defined(HAVE_LINUX_PARPORT_H) || defined(__WIN32__))
    &cable_par,
#endif

Looking at the changes a bit more, it's because defining a macro with no value still makes it defined, so the check in the code ends up not doing what we want.

So, if we don't want to change the code (to check for an actual value, like 1 which cmake uses, not sure about the autotools), only the CMakeLists.txt, we should do that:

if (HAVE_LINUX_PARPORT_H)
    target_compile_definitions(ticables2_objlib PUBLIC HAVE_LINUX_PARPORT_H=1)
endif()
if (HAVE_LINUX_SERIAL_H)
    target_compile_definitions(ticables2_objlib PUBLIC HAVE_LINUX_SERIAL_H=1)
endif()

[davide125]

Thanks! I forgot cmake doesn't like undefined variables. I've retested on my end and confirmed this still does the right thing on Linux.

[adriweb]

No problem, I'm not a CMake expert anyway (maybe there's a shorter/cleaner way to do all that), so I wouldn't have caught it if I hadn't tried :P

[debrouxl]

Thanks :)