clang: enable colored diagnostic output for kernel compilation

[iav]

Summary

• When building kernels with KERNEL_COMPILER=clang, compiler warnings were displayed without color
• The GCC-native flag -fdiagnostics-color=always (set in KCFLAGS) is not reliably honored by clang when invoked through ccache and the kernel build system with LLVM=1
• Added -fcolor-diagnostics (clang's native flag) to the clang-specific extra_warnings to ensure colored output

Test plan

• Built kernel with KERNEL_COMPILER=clang — warnings now have ANSI color codes
• Verify no regressions with default GCC builds

🤖 Generated with Claude Code

Summary by CodeRabbit

• Chores
  • Enhanced compiler output formatting with colored diagnostics support for improved build log readability.

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[coderabbitai]

📝 Walkthrough

Walkthrough

A compiler flag modification in the kernel build script adds color diagnostics support (-fcolor-diagnostics) to the clang compilation warnings configuration, preserving existing error suppression behavior.

Changes

Cohort / File(s)	Summary
Clang compiler configuration lib/functions/compilation/kernel-make.sh	Added -fcolor-diagnostics flag to extra_warnings in the clang path of run_kernel_make_internal function while retaining existing -Wno-error=unused-command-line-argument suppression

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

Poem

🐰 With colors now bright, diagnostics will gleam,
Clang's warnings dance in a vibrant dream,
Red flags and blues to guide the code flow,
Making compiler feedback easier to know! 🌈

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and directly describes the main change: adding colored diagnostic output support for clang during kernel compilation, which matches the primary objective of enabling the -fcolor-diagnostics flag.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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✨ Finishing touches

• 📝 Generate docstrings

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[github-actions]

✅ This PR has been reviewed and approved — all set for merge!