Support LLVM 18-21 for T2C

[jserv]

• Add LLVM version detection macros to mk/toolchain.mk using 'define' for reusability: llvm-config-path, llvm-homebrew-config, detect-llvm-config, llvm-version, llvm-check-libs, llvm-cflags, llvm-libfiles
• Support LLVM 18, 19, 20, and 21 (previously only LLVM 18)
• Add compile-time version check in t2c.c with clear error/warning
• Document MCJIT deprecation status: LLVM 22+ may deprecate MCJIT in favor of ORC JIT; when upgrading, review MCJIT status and LLVMGetInlineAsm signature changes
• Allow user override via LLVM_CONFIG= make variable

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Summary by cubic

Expand T2C LLVM support to versions 18–21 and add reusable detection + compile-time checks to make builds simpler and more reliable. Homebrew installs are handled, and users can override the LLVM binary via LLVM_CONFIG.

• New Features

  • Added LLVM detection helpers in mk/toolchain.mk (detect-llvm-config, llvm-version, llvm-check-libs, llvm-cflags, llvm-libfiles, detect-homebrew-llvm-prefix).
  • Makefile now uses these helpers, sets flags from llvm-config, and adds Homebrew lib path when needed. Clear warnings if libs or llvm-config are missing.
  • t2c.c enforces LLVM 18–21 at compile time (error if <18, warning if >21). Notes MCJIT deprecation risk for LLVM 22+.

• Refactors

  • Moved LLVM detection logic out of the Makefile into mk/toolchain.mk for reuse and readability.
  • Skip the JIT arch check when cross-compiling with emcc. Simplified T2C_OPT_LEVEL default handling.

^{Written for commit b26939d. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 3 files

[jserv]

Benchmarks

Details

Benchmark suite	Current: b26939d	Previous: 82205cb	Ratio
Dhrystone	1597.333 DMIPS	1608.333 DMIPS	1.01
CoreMark	973.382 iterations/sec	958.926 iterations/sec	0.99

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