x86 CPUID compile errors on Windows with Clang and GCC compilers

[p0lymeric]

Prerequisites

• Checked the developer manual
• Checked that your issue isn't already filed: https://github.com/issues?utf8=✓&q=repo%3Alibtom%2Flibtomcrypt

Description

There are some compilation errors relating to recently added x86 CPUID detection code.

ClangCL (Clang 20.1.8):

• Looks like <intrin.h> should be included in files that call __cpuid. (I guess MSVC magically recognizes __cpuid without a header, but ClangCL needs the header.)

<...>\cpp\lib\libtomcrypt\src\hashes\sha2\sha256_desc.c(12,4): error : call to undeclared library function '__cpuid' with type 'void (int *, int)'; <...>
<...>\cpp\lib\libtomcrypt\src\hashes\sha2\sha256_desc.c(12,4): message : include the header <intrin.h> or explicitly provide a declaration for '__cpuid' <...>

MinGW-UCRT64 (GCC 15.2.0) / MinGW-Clang64 (Clang 21.1.7):

• Looks like asm should be changed to __asm__, to allow building without GNU C extensions.
• I wonder if this issue also manifests on other x86 targets (e.g. Linux) that compile with -std=c##.

<...>/cpp/lib/libtomcrypt/src/hashes/sha2/sha256_desc.c:18:5: error: use of undeclared identifier 'asm'
   18 |     asm volatile ("cpuid"
      |     ^~~

I am open to submitting a fix if desired, or an existing contributor could do so. Thanks for the recent work on adding x86 acceleration to the library.

Version

a68fa19 (top of develop tree May 19)