This used to work:

./configure -system-libpng -system-libjpeg -system-pcre 

The new configure script translates them to CMake options automatically, but the ones specifically listed here have changed names. I get the following when I try the:

CMake Warning:
  Manually-specified variables were not used by the project:

    FEATURE_system_libjpeg
    FEATURE_system_libpng
    FEATURE_system_pcre

I see CMake understands the following variables:

• FEATURE_SYSTEM_png instead of FEATURE_SYSTEM_libpng
• FEATURE_SYSTEM_jpeg instead of FEATURE_SYSTEM_libjpeg
• FEATURE_SYSTEM_pcre2 instead of FEATURE_SYSTEM_pcre
• EDIT: FEATURE_pkg_config instead of FEATURE_pkg-config (notice the dash instead of the underscore, the configure script was accepting the option -pkg-config)

Should we rename them to the old names to retain compatibility?

P.S. Haven't searched exhaustively whether more variables are affected.