cmake HAVE_NOVSX examples

InsightSoftwareConsortium/ITK Modules/ThirdParty/ZLIB/src/itkzlib-ng/cmake/detect-intrinsics.cmake :338

check_c_source_compiles(
        "#include <altivec.h>
        int main(void)
        {
            vector int a = vec_splats(0);
            vector int b = vec_splats(0);
            a = vec_add(a, b);
            return 0;
        }"
        HAVE_NOVSX
        )