games/openttd: update OpenTTD to the latest version 13.4
- By popular demand, prefer SDL 2.x by default but leave the option to use the previous stable version
- Drop incomplete work-around for strange Clang bug added in commit f2488f960dc8: the problem is not specific to PowerPC but versions 13.1 and later no longer trigger it (pending investigation)
PR: 272428, 272623
Reported by: portscout, pkg-fallout
Clang bug: https://github.com/llvm/llvm-project/issues/49093