c++/modules: Stream warning suppressions [PR115757]

c++/modules: Stream warning suppressions [PR115757]

Currently we don't stream the contents of 'nowarn_map'; this means that
warning suppressions don't get applied in importers, which is
particularly relevant for templates (as in the linked testcase).

Rather than streaming the whole contents of 'nowarn_map', this patch
instead just streams the exported suppressions for each tree node
individually, to not build up additional locations and suppressions for
tree nodes that do not need to be streamed.

	PR c++/115757

gcc/cp/ChangeLog:

	* module.cc (trees_out::core_vals): Write warning specs for
	DECLs and EXPRs.
	(trees_in::core_vals): Read warning specs.

gcc/ChangeLog:

	* tree.h (put_warning_spec_at): Declare new function.
	(has_warning_spec): Likewise.
	(get_warning_spec): Likewise.
	(put_warning_spec): Likewise.
	* diagnostic-spec.h (nowarn_spec_t::from_bits): New function.
	* diagnostic-spec.cc (put_warning_spec_at): New function.
	* warning-control.cc (has_warning_spec): New function.
	(get_warning_spec): New function.
	(put_warning_spec): New function.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/warn-spec-1_a.C: New test.
	* g++.dg/modules/warn-spec-1_b.C: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>