fix(build): download baseline WebKit for x64 baseline builds

[robobun]

Summary

• When ENABLE_BASELINE=ON is set for x86_64 builds, append -baseline to the WebKit download URL suffix in SetupWebKit.cmake
• Without this fix, baseline Bun links against a WebKit library compiled with AVX/AVX2 instructions, causing SIGILL crashes on CPUs without AVX support
• The baseline suffix placement matches the naming convention from Add baseline x64 Linux builds for CPUs without AVX WebKit#137 which produces the corresponding baseline WebKit artifacts

Context

The ENABLE_BASELINE flag correctly sets -march=nehalem for Bun's own code (CompilerFlags.cmake:32) and marks the binary as baseline (BuildBun.cmake:690), but the WebKit download URL was missing the baseline distinction. This meant baseline Bun was linking against a WebKit built with -march=haswell (AVX2), causing illegal instruction crashes on pre-AVX CPUs.

Note: This fix depends on oven-sh/WebKit#137 being merged to produce the baseline WebKit build artifacts. Until that PR is merged, baseline builds will get a clear download error at build time instead of silently producing a binary that crashes at runtime.

Closes #27090
Also related to #26353, #26635, #26872, #27006

Test plan

• Verified the suffix produces correct download URLs:
  • bun-webkit-linux-amd64-baseline-lto.tar.gz (Linux glibc LTO)
  • bun-webkit-linux-amd64-baseline.tar.gz (Linux glibc)
  • bun-webkit-linux-amd64-musl-baseline-lto.tar.gz (Linux musl LTO)
  • bun-webkit-linux-amd64-musl-baseline.tar.gz (Linux musl)
• Verified non-baseline builds are unaffected (suffix only added when both ENABLE_BASELINE and amd64 arch)
• Verified ARM64 builds are unaffected (baseline is x86_64-only)

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[robobun]

^{Updated 12:54 PM PT - Feb 17th, 2026}

❌ Your commit 3fea0d47 has 3 failures in Build #37472 (All Failures):

• test/js/node/http/node-http-backpressure-max.test.ts - 1 failing on 🍎 13 x64
• test/js/third_party/mongodb/mongodb.test.ts - 1 failing on 🪟 2019 x64
• test/js/third_party/mongodb/mongodb.test.ts - 1 failing on 🐧 25.04 aarch64
• test/js/third_party/mongodb/mongodb.test.ts - 1 failing on 🐧 13 aarch64
• test/js/third_party/mongodb/mongodb.test.ts - 1 failing on 🐧 3.23 x64
• test/js/third_party/mongodb/mongodb.test.ts - 1 failing on 🐧 25.04 x64
• test/js/third_party/mongodb/mongodb.test.ts - 1 failing on 🐧 13 x64
• test/js/third_party/mongodb/mongodb.test.ts - 1 failing on 🐧 3.23 aarch64
• test/js/third_party/mongodb/mongodb.test.ts - 1 failing on 🐧 13 x64-asan
• test/js/third_party/mongodb/mongodb.test.ts - 1 failing on 🍎 14 x64
• test/js/third_party/mongodb/mongodb.test.ts - 1 failing on 🍎 14 aarch64
• test/js/third_party/mongodb/mongodb.test.ts - 1 failing on 🍎 13 aarch64
• test/js/third_party/mongodb/mongodb.test.ts - 1 failing on 🍎 13 x64
• cmake/targets/BuildBun.cmake - cmake error on 🐧 x64-musl-baseline - build-zig
• cmake/targets/BuildBun.cmake - cmake error on 🐧 x64-baseline - build-zig
• cmake/targets/BuildBun.cmake - cmake error on 🪟 x64-baseline - build-zig
• cmake/targets/BuildBun.cmake - cmake error on 🐧 x64-baseline - build-cpp
• cmake/targets/BuildBun.cmake - cmake error on 🐧 x64-musl-baseline - build-cpp
• cmake/targets/BuildBun.cmake - cmake error on 🪟 x64-baseline - build-cpp
• cmake/targets/BuildBun.cmake - cmake error on 🪟 x64-baseline - build-cpp

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🧪   To try this PR locally:

bunx bun-pr 27091

That installs a local version of the PR into your bun-27091 executable, so you can run:

bun-27091 --bun

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

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Walkthrough

Adds conditional logic to append a "-baseline" suffix to the WebKit build suffix when the ENABLE_BASELINE flag is enabled and the target architecture is amd64. This suffix is applied after musl suffix handling and before debug/lto logic.

Changes

Cohort / File(s)	Summary
WebKit Build Configuration cmake/tools/SetupWebKit.cmake	Adds conditional baseline suffix to WEBKIT_SUFFIX when ENABLE_BASELINE is true for amd64 architecture, affecting final WEBKIT_NAME and derived filenames.

🚥 Pre-merge checks | ✅ 2

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately and clearly describes the main change: appending '-baseline' to WebKit download URLs for x64 baseline builds to fix SIGILL crashes.
Description check	✅ Passed	The description exceeds the template requirements with comprehensive sections covering what the PR does, why it's needed, context, related issues, and detailed test verification.

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[claude]

Code Review

Newest first

✅ 3fea0 — Looks good!

Reviewed 1 file in cmake/tools/: Fixes the CMake build configuration to download the correct baseline WebKit binary (compiled without AVX/AVX2 instructions) when building Bun with ENABLE_BASELINE=ON on x86_64, preventing SIGILL crashes on older CPUs that lack AVX support.

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