biology/py-scikit-bio: fix build on powerpc64

GCC is also necessary on powerpc64:
In file included from skbio/alignment/_ssw_wrapper.c:626:
In file included from skbio/alignment/_lib/ssw.h:17:
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:50:12: error: invalid conversion between vector type '__m64' (vector of 1 'long long' value) and integer type 'int' of different size

return (__m64)__builtin_ia32_vec_init_v2si(__i, 0);