cksum,wc: clean up hw capability checking

cksum,wc: clean up hw capability checking

* src/cksum.c (cksum_pclmul) [!CRCTAB && !USE_PCLMUL_CRC32]:
Remove macro.
(cksum_fp): No longer file-scope.
(pclmul_supported): Define only if USE_PCLMUL_CRC32.
This omits the debug output "using generic hardware support"
for simplicity and consistency with wc’s output.
(crc_sum_stream) [!USE_PCLMUL_32]: No need for static function pointer.
* src/wc.c (wc_lines_p) [USE_AVX2_WC_LINECOUNT]: No longer file-scope.
(wc) [USE_AVX2_WC_LINECOUNT]: Check for avx2 support at most once,
which was surely the code’s original intent.
(wc) [!USE_AVX2_WC_LINECOUNT]: No need for static function pointer.