* cpplex.c (null_cleanup): Delete.
(cpp_pop_buffer): Do the work that was done in the cleanups
here. Call _cpp_unwind_if_stack from here.
(_cpp_expand_to_buffer, cpp_scan_buffer_nooutput,
cpp_scan_buffer): Run until we see CPP_EOF and the top of
stack is the buffer _below_ the one we stacked.
(cpp_get_token): Always pop an exhausted buffer. Return
CPP_EOF unless it's a macro buffer. Don't call _cpp_handle_eof.
* cpplib.c (skip_if_group): Don't call cpp_get_token to
increment the line number.
(_cpp_handle_eof): Rename to _cpp_unwind_if_stack.
* fix-header.c (read_scan_file) [parsing getchar()]: Run until
we see CPP_EOF and the top of stack is the buffer _below_ the
one we stacked.
* scan-decls.c: Likewise.