make-docfile: minor fixes and cleanups

make-docfile: minor fixes and cleanups

* lib-src/make-docfile.c: Include c-ctype.h.
(read_c_string_or_comment, write_c_args, scan_c_stream, skip_white)
(read_lisp_symbol, scan_lisp_file):
Prefer c_isspace etc. to listing characters by hand.
(read_c_string_or_comment): Simplify.
(scan_c_stream, read_lisp_symbol): Use true for boolean 1.
(scan_c_stream): Fix typo (c >= 'Z' && c <= 'Z').
Minor rewrites to avoid duplicate code.
(scan_c_stream, read_lisp_symbol, scan_lisp_file):
Avoid infloop if at EOF.
(skip_white, read_lisp_symbol): Don’t stuff getc result into
‘char’, as this mishandles EOF.