Some time before working on cproto, I had hand-built lint-libraries for X11 on SunOS. The vendor did not distribute usable lint-libraries: the corresponding ".ln" files were zero-length, and there were no text-files to match. Moreover, X11 did not build lint-libraries that matched the sources (many functions were missing or had different parameters). Since the llib-* text files are basically the ".c" files with the function-bodies emptied, it was possible to edit them and produce correct lint library source.
But that is very time-consuming, and not something that I would do more than once. Modifying cproto was a better solution; I used the resulting lint-libraries for several years.
Currently I use cproto to generate lint-libraries for ncurses. I also make occasional fixes, generally as a branch, e.g., "4.7a". See the changelog for details.