buildworld falure: truncated or malformed archive

[Ryan Stone]

I'm trying to update an old (~May 2018) -head system to the latest,
but I'm getting a persistent error during buildworld:

ld: error: /usr/obj/usr/src/amd64.amd64/lib/clang/libclang/libclang.a:
could not get the member for symbol
_ZN5clang17MultiplexConsumerC1ENSt3__16vectorINS1_10unique_ptrINS_11ASTConsumerENS1_14default_deleteIS4_EEEENS1_9allocatorIS7_EEEE:
truncated or malformed archive (terminator characters in archive
member "dC" not the correct "`\n" values for the archive member header
for tOutputExprEj

I seem to recall something about libarchive or ar having a bug
creating archives > 4GB, but I tried doing a "make install" from
lib/libarchive and usr.bin/ar and doing a rebuild, and that doesn't
seem to have resolved the issue.  I also made sure to try a build with
a clean /usr/obj with no success.  Any ideas how I can get past this?