[MSVC] Replace #warning with compatible directives for MSVC

[FrankXie05]

Summary

This PR addresses an issue where the #warning directive in cpuid_main.c is not supported by MSVC, causing a fatal error (C1021: invalid preprocessor command 'warning'). The warning is used to notify users when libcpuid is built on unsupported CPU architectures, such as ARM.

Changes Made

• Replaced #warning with a compiler-specific directive.
  • For MSVC (_MSC_VER), used #pragma message to generate a similar warning message.
  • For other compilers, retained #warning for compatibility.
• The warning is conditionally triggered only for ARM architectures (__arm__ or __aarch64__).

Rationale

This change ensures that libcpuid can be built successfully on MSVC while still providing meaningful warnings for unsupported CPU architectures. It improves cross-platform compatibility without changing the behavior for compilers that support #warning.

Test Plan

• Verified successful compilation on MSVC with ARM architecture.
• Ensured the warning message appears in build logs for both MSVC and other compilers.

Example of New Warning

On MSVC:

Related PR: microsoft/vcpkg#42117

[TheTumultuousUnicornOfDarkness]

I was not able to build with MSVC on ARM due to the lack of ARM-based public Runners on GitHub. Thanks for the fix!