Replace 4 hardcoded `perl` invocations with `${PERL_EXECUTABLE}` from
find_package(Perl) so builds work when perl isn't in PATH or the wrong
perl would be found (NixOS, custom installs, Homebrew vs system).
Also: fix ZMCONFGEN_RESULT variable case mismatch in error message,
remove deprecated IMMEDIATE keyword from configure_file(), bump
cmake_minimum_required from 3.5 to 3.12 (C++17 requires 3.9+), and
remove dead C++11 fallback for CMake < 3.8 in ConfigureBaseTargets.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
The zm-dependency-interface target sets compiler flags in a way suitable for external dependencies.
This means mainly to disable compile warnings since they concern upstream and not us.
zm-compile-option-interface:
Use to set various compiler/linker flags
zm-feature-interface:
Use to set required compiler features.
See https://cmake.org/cmake/help/latest/prop_gbl/CMAKE_CXX_KNOWN_FEATURES.html
zm-warning-interface:
Use to set compiler warning flags. If need be a zm-no-warning-interface can be added which suppresses all warning for targets linked against it. Useful for in-tree dependencies from which we don't want compiler warnings.
zm-core-interface:
That's the interface one should normally link against to get all the options.