games/openclonk: Fix link on 14-CURRENT i386

Fix build on 14-CURRENT i386 by disabling dynamic relocation checks with
lld 15.

While here, since this port is BROKEN_powerpc64, remove the old powerpc
build flags.

PR: 271500
MFH: 2023Q2
(cherry picked from commit 35a33a5fa5b5da7b48d7401435403461796680e0)