[9.18] Add semantic patch to explicitly cast chars to unsigned for ctype.h
Add a semantic patch to catch all the places where we pass 'char' to the <ctype.h> family of functions (isalpha() and friends, toupper(), tolower()). While it generally works because the way how these functions are constructed in the libc, it's safer to do the explicit cast.
(cherry picked from commit 5ec65ab5)
Closes #4327 (closed)
Backport of !8325 (merged)
Edited by Ondřej Surý