mariadb105-server will not build for systems lacking sbrk, and needs the patch-MDEV-15961 file that is also in mariadb103-server and mariadb104-server.
Thanks for reporting, adding the patch...
A commit references this bug:
Date: Sun Jul 19 20:19:56 UTC 2020
New revision: 542596
databases/mariadb105-server: Fix build for i386
* pet portlint
* i386 requires gcc 
* Fix stacktrace 
PR: 247535 , 247957 
Reported by: Raymond Quakkelaar <r quakkelaar quaras nl> , Naram Qashat <cyberbotx cyberbotx com> 
Started out with a new port with as few as possible patches.
Keep reporting when things are missing!
Just as an FYI, this is FINALLY fixed upstream, and will be in the next patch release of all MariaDB versions.