a68: introduce a68_file_size and a68_file_read

a68: introduce a68_file_size and a68_file_read

This commit introduces two new utility functions that replace some
ad-hoc infrastructure in the scanner.

Signed-off-by: Jose E. Marchesi <jemarch@gnu.org>
gcc/algol68/ChangeLog

	* a68.h: Prototypes for a68_get_file_size and a68_file_read.
	* a68-parser-scanner.cc (a68_file_size): New function.
	(a68_file_read): Renamed from io_read.
	(get_source_size): Deleted function.
	(include_files): Use a68_file_size and a68_file_read.