Default to building wxOSX, not wxiOS, under Apple ARM platforms

Now that desktop Macs using ARM exist, we should default to building the
normal, macOS-targeting, port on them and not wxiOS any more.

This is a backwards incompatible change, but it shouldn't affect many
people, so should hopefully be fine.

docs/changes.txt

@@ -189,6 +189,10 @@ INCOMPATIBLE CHANGES SINCE 3.1.3:
   aliases for the libraries have been added using the 'wx::' namespace. For
   example, the core library is now named wxcore and has alias wx::core.
 
+- Building on ARM Apple platforms using configure now targets macOS by
+  default, and not iOS. Please use --with-osx_iphone explicitly if you need
+  the latter.
+
 
 3.1.3: (released 2019-10-28)
 ----------------------------