Use bool for "parse_completion"

Use bool for "parse_completion"

Some spots in GDB already use bool for "parse_completion", but a few
were still using int.  This patch updates these to bool.

I'm checking this in.

gdb/ChangeLog
2021-03-10  Tom Tromey  <tromey@adacore.com>

	* parser-defs.h (parser_state): Change completion to bool.
	<parse_completion>: Likewise.
	* ada-lang.h (ada_find_operator_symbol, ada_resolve_funcall)
	(ada_resolve_variable, ada_resolve_function): Update.
	* ada-lang.c (ada_find_operator_symbol): Change
	parse_completion to bool.
	(ada_resolve_funcall, ada_resolve_variable)
	(ada_resolve_function): Likewise.