Enable SSE2 options by default
Enable SSE2 options by default

The builds from the original author used SSSE3 in their default build but it
seems it is only supported by fairly recent Intel processors. Thus setting it
to SSE2 instead by default should be better for people building it from source.

mupen64plus/mupen64plus-rsp-cxd4,mupen64plus/mupen64plus-rsp-cxd4,mupen64plus/mupen64plus-rsp-cxd4