archivers/c-blosc2: fix build on powerpc64*

Build was broken with GCC with:
/wrkdirs/usr/ports/archivers/c-blosc2/work/c-blosc2-2.15.1/blosc/shuffle-altivec.c: At top level:
/wrkdirs/usr/ports/archivers/c-blosc2/work/c-blosc2-2.15.1/blosc/shuffle-altivec.c:427:12: error: conflicting types for 'is_shuffle_altivec'; have 'vector bool int' {aka 'const vector(4) bool int'}

427 | const bool is_shuffle_altivec = true;
    |            ^~~~~~~~~~~~~~~~~~

Go back to building with Clang and actually fix it - Clang has issues with
types like vector uint8_t but accepts vector unsigned char, which this
this commit changes.