We've compiled it since the LLVM 13 import in 2021, but for some reason
never exported it. A user of CheriBSD recently caused Morello LLVM to
emit a reference to it so finish the job and export it.
Fixes: 6e75b2fbf9a0 ("Merge llvm-project release/13.x llvmorg-13.0.0-rc1-97-g23ba3732246a")
MFC after: 1 week
Sponsored by: DARPA, AFRL
See also: https://github.com/CTSRD-CHERI/cheribsd/issues/2614