audio/madronalib: fix build on powerpc64le

Use GCC with its SSE translation:
In file included from /wrkdirs/usr/ports/audio/madronalib/work/madronalib-1.6-1016-g103895f/source/DSP/MLDSPMathSSE.h:32:
In file included from /usr/lib/clang/11.0.1/include/emmintrin.h:13:
In file included from /usr/lib/clang/11.0.1/include/xmmintrin.h:13:
/usr/lib/clang/11.0.1/include/mmintrin.h:33:5: error: use of undeclared identifier 'builtin_ia32_emms'; did you mean 'builtin_isless'?

__builtin_ia32_emms();