Update to 1.4.53. From the changelog:

* [mod_cml,mod_flv_streaming] fix NULL ptr deref
* [mod_simple_vhost] t/test_mod_simple_vhost
* [mod_evhost] split uri handler func for testing
* [mod_evhost] restructure for unit tests
* [mod_evhost] t/test_mod_evhost
* [mod_access] restructure for unit tests
* [mod_access] t/test_mod_access
* [tests] include first.h and NDEBUG early
* [core] use kill_signal for gw_proc_kill()
* [tests] t/test_keyvalue
* [tests] some test config cleanup
* [tests] update skip count in mod-fastcgi.t
* [multiple] reduce initial buffer sz if large POST (fixes #2922)
* [mod_fastcgi] fix NULL ptr deref from bugfix #2922 (fixes #2923)
* [tests] more test config cleanup
* [core] perf: incremental hash of pathname w/o copy
* [core] perf: reuse buffer to redirect to directory
* [core] do not free() reused buffer
* [core] use connected sock port in dir redirect
* [core] http_response_buffer_append_authority()
* [core] use con->server_name for dir redir
* [core] memeq compare rounded to 64, not next 1M
* [core] define MD5_DIGEST_LENGTH 16
* [mod_auth] permit additional auth backends to load
* [core] send Connection: close if reqbody not read (fixes #2924)
* [core] cache rev DNS for localhost for dir redir
* [doc/conf] resolve some mime type conflicts from debian buster,
  regenerate mime.conf
* [core] move winsock init to network_init()
* [core] move /dev/stdin graceful restart handling
* [core] network_srv_sockets_append() shared code
* [core] systemd socket activation support
* [build] autotools: try mysqlclient.pc and mariadb.pc (fixes #2925)
* [mod_expire] look up expire fallback "" explicitly
* [multiple] calloc match ptr type (clang --analyze)
* [multiple] quiet clang --analyze where trivial
* [mod_webdav] compare COPY, MOVE Destination scheme
* [core] con->uri.scheme is maintained lowercase
* [mod_openssl] ALPN and acme-tls/1 (fixes #2931)
* [core] Fix recursive include_shell invocations
* [mod_openssl] ssl.privkey directive (optional)


(schmonz)