Merge topic branch t/build into pu

Started on 2023-06-21

This series simplifies the build system quite a bit. The bulk of the
series consists of the commits which move the logic to construct
the object list of the paraslash executables from configure.ac to
Makefile.real.

<!--
- Simplification of the build system. The only visible effect is
  that configure no longer prints a summary at the end.
-->

* refs/heads/t/build:
  build: Rename all_objs -> dep_objs.
  build: No longer check for CRYPTO_cleanup_all_ex_data().
  build: Construct list of executables in Makefile.
  build: Construct audioc object list in Makefile.
  build: Construct write object list in Makefile.
  build: Construct play object list in Makefile.
  build: Construct afh object list in Makefile.
  build: Construct filter object list in Makefile.
  build: Construct recv object list in Makefile.
  build: Construct gui object list in Makefile.
  build: Construct mixer object list in Makefile.
  build: Construct audiod and client object list in Makefile.
  build: Construct server and upgrade_db object list in Makefile.
  build: Simplify condition for building para_server.
  build: Simplify ogg helpers of configure.ac.
  build: Remove AUDIOD_AUDIO_FORMATS_ENUM.
  build: Remove _errlist in shell variables of configure.ac.
  build: yy_src_dir and yy_build_dir can be simply expanded.
  build: Remove info about ucred from configure output.