Add some constness to avoid some warnings.
Remove use register keyword.
Deal with missing/unneeded extern/prototypes.
Some minor type changes/casts to avoid warnings.
Reviewed by: md5
the new content size fits into the sbuf, instead of assuming
that allocating twice the old size is enough.
- Use memmove(3) rather than strcpy(3) to copy overlapping
strings.
PR: bin/39930
