jpeg-xl: record build failure with Apple Clang build 1000

[whitslack]

jpeg-xl fails to build with Apple Clang 1000:

lib/jxl/enc_fast_lossless.cc:369:7: error: invalid cpu feature string for builtin
  if (__builtin_cpu_supports("avx512vbmi2")) {
      ^                      ~~~~~~~~~~~~~

Adding an appropriate fails_with block lets Homebrew use llvm_clang instead, which works.

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• Have you followed the guidelines for contributing?
• Have you ensured that your commits follow the commit style guide?
• Have you checked that there aren't other open pull requests for the same formula update/change?
• Have you built your formula locally with brew install --build-from-source <formula>, where <formula> is the name of the formula you're submitting?
• Is your test running fine brew test <formula>, where <formula> is the name of the formula you're submitting?
  • No, because the test code is trying to execute ENV.cc, which evaluates to llvm_clang, but no executable by that name is found in my PATH. Either the ENV.cc variable should be set to /usr/local/Homebrew/Library/Homebrew/shims/mac/super/llvm_clang, or /usr/local/Homebrew/Library/Homebrew/shims/mac/super should be temporarily appended to PATH while running the test.
• Does your build pass brew audit --strict <formula> (after doing brew install --build-from-source <formula>)? If this is a new formula, does it pass brew audit --new <formula>?

[carlocab]

Thanks!