Allow filtering of detect headers without messing up dependency detection

[vchuravy]

In MLIR.jl I had:

headers = detect_headers(libclang_header_dir, args)
filter!(h->!endswith(h, "Python/Interop.h"), headers)

This caused me to skip some other headers that were only included in Interop.h.

x-ref: https://github.com/JuliaLabs/MLIR.jl/pull/10