sysutils/libcpuid: update to version 0.6.1, use upstream release archive

While few hundreds bytes larger, distfile is more cache-friendly (mtime
remains constant unlike for tarballs generated on the fly by GitHub) and
comes properly bootstrapped, allowing to drop `autoreconf' item from the
USES list.

Remove ONLY_FOR_ARCHS limitation: while currently support is limited for
x86 CPUs, it builds everywhere and gracefully handles unknown ones, thus
unbreaking more of those reverse dependencies mentioned in 9482644374c1.

PR: 267277 (partially applied)