Move cpuid.h -> cpu_id.h

[joerowell]

What's this?

This PR fixes a build issue on some platforms (in particular, one of our nodes).

What's the exact issue?

The lookup mechanism for angle-bracketed include directives (i.e. #include <cpuid.h>) is implementation defined. In some settings, the lookup mechanism will search the current directory before any system paths. This can cause build issues for this project that look as follows:

cpuid.h:8:27: error: ‘__cpuid_count’ was not declared in this scope
          8 |   #define CPUID(info, x)  __cpuid_count(x, 0, info[0], info[1], info[2], info[3])
            |                           ^~~~~~~~~~~~~

The reason why is because the #include<cpuid.h> is seemingly including cpuid.h itself (the #pragma once probably guards this in a way that #ifndef wouldn't) and thus the __cpuid_count function is never defined.

It turns out that renaming cpuid.h to cpu_id.h is sufficient to fix the issue.

[vmarkovtsev]

FYI: another way to fix was to insert #include_next <cpuid.h> into our cpuid.h.