New compile scripts for ngspice executable and shared library,
using gcc-11 from Homebrew.
All relevant options are included (readline, openmp, X11 graphics etc.)
--with-readline=<location> may be given instead of --with-readline=yes
This is required when on macOS readline is installed from Homebrew.
Standard Xcode readline in macOS is not compatible with ngspice.
If --with-readline=yes is given, there is no change of behaviour
compared with previous releases.
Holger Vogt