* Fixes a critical bug in the Arm64 port (related to Issue #3, which is
   unfixed in Xcode toolchains in common use).
 * Adds a new configure option ```--with-darwin-extra-rpath=``` which allows
   a distribution to prepend a run path to the list automatically added by
   the compiler.  This is to allow for cases where the distribution refers to
   installed libraries using symlinks from outside the installation paths.
 * Resolves a potential issue with library references where a minor GCC
   version is replaced by the next and the old version is deleted.
 * Amends some of the system version processing to handle changes expected in
   macOS 13+.
 * Improves interoperability with clang in mixed code projects.