games/openclonk: fix build on powerpc64le

In file included from /wrkdirs/usr/ports/games/openclonk/work/openclonk-release-8.1-src/thirdparty/blake2/blake2b.c:28:
In file included from /usr/lib/clang/14.0.5/include/ppc_wrappers/emmintrin.h:43:
/usr/lib/clang/14.0.5/include/ppc_wrappers/xmmintrin.h:31:2: error: "Please read comment above. Use -DNO_WARN_X86_INTRINSICS to disable this error."