Add a check for term.h

If term.h is present, use that instead of defining prototypes for the
terminfo functions in terminfo-core.c. This causes problems on certain
platforms (e.g. Apple aarch64) due to the functions being prototyped as
non-variadic but called as variadic. If term.h isn't found, it falls
back to the old behaviour.

Fixes #1238.

meson.build

@@ -525,6 +525,7 @@ headers = [
   'sys/time.h',
   'sys/utsname.h',
   'dirent.h',
+  'term.h',
   'unistd.h',
 ]
 foreach h : headers