wxWidgets variant does not build with wxGTK-3.0

[barracuda156]

Describe the bug
Trying to build Erlang with wxWidgets support via wxGTK-3.0 fails.

To Reproduce
Run the build, get:

 CXX	powerpc-apple-darwin10.0.0d2/wxe_impl.o
wxe_impl.cpp: In member function ‘virtual bool WxeApp::OnInit()’:
wxe_impl.cpp:204: error: ‘MacSetCommonMenuBar’ is not a member of ‘wxMenuBar’
wxe_impl.cpp:205: error: ‘class wxMenuBar’ has no member named ‘MacInstallMenuBar’
make[3]: *** [powerpc-apple-darwin10.0.0d2/wxe_impl.o] Error 1

It looks like it is hardcoded to expect Cocoa.

Expected behavior
It is desirable to have it supported, since Cocoa version of wxWidgets 3.x is broken on a number of macOS versions (3.2 does not build on many, 3.0 builds but does not work correctly on < 10.9 or so).

Affected versions
26.2.3

Additional context
Macports build system.

[barracuda156]

Commenting out that chunk in wxe_impl.cpp lets build proceed, but then it fails on:

Undefined symbols:
  ".objc_class_name_NSAutoreleasePool", referenced from:
      literal-pointer@__OBJC@__cls_refs@NSAutoreleasePool in wxe_ps_init.o
  ".objc_class_name_NSImage", referenced from:
      literal-pointer@__OBJC@__cls_refs@NSImage in wxe_ps_init.o
  "_NSApp", referenced from:
      _NSApp$non_lazy_ptr in wxe_ps_init.o
  ".objc_class_name_NSMutableString", referenced from:
      literal-pointer@__OBJC@__cls_refs@NSMutableString in wxe_ps_init.o
  ".objc_class_name_NSRunningApplication", referenced from:
      literal-pointer@__OBJC@__cls_refs@NSRunningApplication in wxe_ps_init.o
ld: symbol(s) not found
collect2: ld returned 1 exit status

Perhaps just macros are currently wrong, and all those #ifdef _MACOSX should not be used on macOS with wxGTK.

[barracuda156]

BTW, I guess 46320cb commit refers to a bug in wxWidgets 3.0 due to which they are broken, but the problem is that later versions are broken completely, i.e. not able to build.

[dgud]

I'll not work on this send a PR if you want this supported.