In #28519 / 791ce593ce065cf074edf1509ff52ebc69136d9e I made linux
headers be intended to be used from the stage stage, as it would be if
it were a library containing headers and code. I forgot to update glibc,
however, so it was incorrectly using headers for the build platform, not
host platform.
This fixes that, basically reverting a small portion of changes I made a
few months ago in 25edc476fd9fe1bd8bedf571d218ba4f27fb5a27 and its
parent.
No native hashes are changed.
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