Compilation on macOS

[Carlo Cabrera]

Last year, Brook Milligan submitted a patch for macOS. [1] Is there any
chance that this could be included in the codebase?

The patch resolves problems with Homebrew packaging of QScintilla for
Apple Silicon, where we use the non-standard installation prefix
/opt/homebrew. [2] Without it, attempting to import the Qsci library in
Python produces the following error:

   ==> /opt/homebrew/opt/python at 3.9/bin/python3 test.py
   Traceback (most recent call last):
     File "/private/tmp/qscintilla2-test-20210123-5191-lvsige/test.py", line 1, in <module>
       import PyQt5.Qsci
   ImportError: dlopen(/opt/homebrew/lib/python3.9/site-packages/PyQt5/Qsci.so, 2): Library not loaded: @rpath/libqscintilla2_qt5.15.dylib
     Referenced from: /opt/homebrew/lib/python3.9/site-packages/PyQt5/Qsci.so
     Reason: image not found

The patch also seems to have resolved issues encountered by MacPorts. [3]

[1] https://www.riverbankcomputing.com/pipermail/qscintilla/2020-March/001444.html
[2] https://github.com/Homebrew/homebrew-core/pull/69653
[3] https://github.com/macports/macports-ports/pull/7790

P.S. Apologies if you’re getting this twice. I’ve resent it because I
suspect my first message was caught by the spam filter.