erlang: add devel branch for 17.0-rc2

OTP 17.0 is a significant release, introducing a number of incompatible changes, including default utf-8 format for source files, but also, finally, compatibility with wxwidgets 3.0.0. This makes all the cool erlang UI debugging tools work OOTB on OSX.

This patch allows a simple:

```
brew update
brew install wxmac --disable-monolithic
brew install --with-wx --no-docs -v --devel erlang
 ```

Issues:

- I don't know how to point the devel branch to different doc urls
- is there a way to tell homebrew that wxmac as a dependency *must* be built with the `--disable-monolithic` flag, and ideally check for that at erlang build time?

<3 your work brewmeisterins and brewmeisters!