A documentação na INSTALAÇÃO no github inclui as seguintes notas:
--enable-pcre:
Zsh has a module which allows the pcre regular expression library to be used via shell builtins. Compiling this library into the shell with dynamic loading (the default where available) produces a dependency on the library libpcre.so. This is a problem on systems where zsh needs to be available at boot before the directory containing libpcre.so (for example /usr/lib or /usr/local/lib) is mounted. For this reason, pcre support will only be searched for if the option --enable-pcre is passed to configure.
Portanto, a opção está controlando se o zsh
funcionará como um shell de nível de "sistema" que pode operar sem dependências externas (como a pasta lib sendo desmontada).
Quanto ao Módulo gdbm , a documentação indica
The zsh/db/gdbm module is used to create "tied" associative arrays that interface to database files. If the GDBM interface is not available, the builtins defined by this module will report an error. This module is also intended as a prototype for creating additional database interfaces, so the ztie builtin may move to a more generic module in the future.