Extern functions were missing attributes such as "readonly" on
non-optional pointers, and "byval" which is required to match C ABI.
Follow-up from bf28765a975355c27558eaa86cf00ccb29b663a7.
closes #12683
fb81ba8762Andrew Kelley committed on 8/30/2022, 9:45:03 PMparent1e21876