[utils][filecheck-lint]: speedup filecheck_lint (#94191)

For example:
clang\test\OpenMP\task_codegen.cpp:  0m29.570s -> 0m0.159s
clang\test\Driver: 4m55.917s -> 1m48.053s

Most win from big files.

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Co-authored-by: klensy <nightouser@gmail.com>