test: disallow llvm-bcanalyzer and use new macro

[compnerd]

This ensures that we use the correct llvm-bcanalyzer from the just built compiler tools.

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[etcwilde]

Missed a test using the llvm-bcanalyzer:

[2026-04-10T01:56:51.991Z] # .---command stdout------------
[2026-04-10T01:56:51.991Z] # | *** Do not use llvm-bcanalyzer in tests; use %llvm-bcanalyzer. ***
[2026-04-10T01:56:51.991Z] # `-----------------------------
[2026-04-10T01:56:51.991Z] # executed command: exit 1
[2026-04-10T01:56:51.991Z] # .---command stderr------------
[2026-04-10T01:56:51.991Z] # | 'exit': command not found
[2026-04-10T01:56:51.991Z] # `-----------------------------
[2026-04-10T01:56:51.991Z] # error: command failed with exit status: 127

Will need to update swift/validation-test/Serialization/bridging-header-first.swift.

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