[bug] HEAD does not compile in ARM

[AndersonTorres]

Hello! I am Anderson, one of many nixpkgs maintainers in my spare time.

Now we use a CI bot, and according to it UCG does not compile on ARM64 machines:

https://logs.nix.ci/?key=nixos/nixpkgs.143708&attempt_id=8ca3dbc9-e4e9-4559-a751-5f17aea73b10

cpuidex.cpp:25:10: fatal error: cpuid.h: No such file or directory
   25 | #include <cpuid.h>  // Need this because clang doesn't support __builtin_cpu_supports().
      |          ^~~~~~~~~
compilation terminated.
make[3]: *** [Makefile:558: libext_la-cpuidex.lo] Error 1
make[3]: Leaving directory '/build/source/src/libext'
make[2]: *** [Makefile:889: all-recursive] Error 1
make[2]: Leaving directory '/build/source/src'
make[1]: *** [Makefile:794: all-recursive] Error 1
make[1]: Leaving directory '/build/source'
make: *** [Makefile:568: all] Error 2

[gvansickle]

Reopening this issue, as it's a legitimate issue that I've not yet addressed. ucg should build on ARM64, but as of now it does not.