doc: document sticky-EOF issue * doc/posix-functions/fgetc.texi (fgetc): * doc/posix-functions/fgets.texi (fgets): * doc/posix-functions/fread.texi (fread): * doc/posix-functions/fscanf.texi (fscanf): * doc/posix-functions/getc.texi (getc): * doc/posix-functions/getchar.texi (getchar): * doc/posix-functions/scanf.texi (scanf): Mention that glibc and default Solaris do not conform to C99 and POSIX-2001 or later, with respect to how getchar etc. behave when feof reports nonzero.