Fix OSX CD build

[dmalec]

The OSX CD build started producing executables which will not run on OSX 10. systems. My working hypothesis is:

1. GitHub has largely moved the macOS-latest build machines to macOS-12 already.
2. OSX 12 needs to have -mmacosx-version-min set to 10.x for compiling and linking in order to produce an executable for 10.x.
3. This can be done as a side effect of compiling wxWidgets with --with-macosx-version-min=10.x and then using that version of wxWidgets macros during configuration of ucblogo.
4. This can also be done by explicitly setting -mmacosx-version-min=10.x prior to compiling logo.

This PR includes two changes:

1. Instead of installing wxWidgets via brew, it installs from the cached copy of wxWidgets. This solves a problem where configure was not finding the WX_CONFIG_CHECK macro.
2. Explicitly setting the value of -mmacosx-version-min prior to compiling logo. This is a bit belt and suspenders; however, it should prevent a change in the way wxWidgets is managed from impacting the compatibility of the executable build.

[jrincayc]

Reviewed and approve