games/openomf: Fix build with non-x86 (non-SSE) architectures

SSE is only available on x86 platforms and forcing it breaks compilation on other platforms.

Clang on 12.0-RELEASE on amd64 enables SSE by default anyway and not-specifying -msse allows to build this port on other, non-SSE architectures.

Also add USES=sdl.

PR: 240093
Approved by: devel@stasyan.com (maintainer), linimon (mentor)