build-tool provided args must be considered first by cc, etc. Generally this already occurred for -I flags, because most of our -I flags were -isystem. However it didn't occur for keg-only flags and -L paths.
This was an error.
I amended the refurbishment code to ensure any paths we want to control the order of are thoroughly scrubbed out of the build-tool provided args. This ensures reliability for our builds.
However this path-scrubbing should always occur, even during configure (I am fairly sure of this). So more work is required.
FixesHomebrew/homebrew#14781.