graphics/openshadinglanguage: fix build on non-x86

In file included from /wrkdirs/usr/ports/graphics/openshadinglanguage/work/OpenShadingLanguage-1.12.6.2/src/include/OSL/mask.h:7:
In file included from /usr/lib/clang/13.0.0/include/immintrin.h:17:
/usr/lib/clang/13.0.0/include/mmintrin.h:33:5: error: use of undeclared identifier '__builtin_ia32_emms'; did you mean '__builtin_isless'?
    __builtin_ia32_emms();