Compilation instructions for wxWidgets on macOS

@lpugin

re: https://github.com/DDMAL/aruspix/wiki/03-%E2%80%93-Aruspix-Command-line

The instructions on the wiki for compiling wxWidgets won't work on the macOS 10.14 (Mojave), as the 32 bit headers have all been removed, and the SDK for the default minimum macOS version that wxWidgets expects is also no longer present.

I suspect this is only a problem on a fresh install of 10.14, as an upgraded system will probably have all of the legacy libraries/SDK (?). Not sure, but this bit me working on a laptop that came with Mojave installed.

Two things need to be changed in the `configure` command in order to compile on macOS 10.14 for a 64 bit architecture:
- change `-arch i386` to `-arch x86_64`
- add flag `--with-macosx-version-min=10.14` (or whatever the minimum supported SDK is on your platform

The following works fine for me:

```
../configure LDFLAGS="-arch x86_64" OBJCFLAGS="-arch x86_64" OBJCXXFLAGS="-arch x86_64" CFLAGS="-arch x86_64" CXXFLAGS="-arch x86_64" CPPFLAGS="-arch x86_64" --disable-shared --with-libjpeg=builtin --with-libpng=builtin --disable-universal-binary --enable-debug --disable-gui --disable-unicode --with-macosx-version-min=10.14
```

Perhaps this could be presented in the wiki as an alternate command for newer systems?

Open the Aruspix wiki page linked in the issue, especially the wxWidgets compilation instructions. Confirm the existing configure command and document the supplied macOS 10.14 64-bit command as an alternate for newer systems; done means the wiki explains the applicable flags and remains understandable for older setups.

Written by the indexing model from the issue text.