translate-c prints to stderr rather than sending error bundle to parent process, resulting in terminal warnings

[andrewrk]

Among other problems, this causes translate-c warnings to be detected as failures by the build system, such as:

warning: TODO: implement 'visibility' attribute for functions [-Wattribute-todo]

Instead, it should follow a similar code path as CObject.Diag.Bundle.parse in the clang execution logic. This way, warnings can be ignored when doing translate-c and errors can be integrated properly with other Compilation errors during @cImport.

This is a follow-up task from #24497.

[squeek502]

Logic for this sort of thing exists in resinator:

zig/lib/compiler/resinator/main.zig

Lines 887 to 957 in c50aa2b

	fn aroDiagnosticsToErrorBundle(
	gpa: std.mem.Allocator,
	fail_msg: []const u8,
	comp: *aro.Compilation,
	) !ErrorBundle {
	@branchHint(.cold);
	var bundle: ErrorBundle.Wip = undefined;
	try bundle.init(gpa);
	errdefer bundle.deinit();
	try bundle.addRootErrorMessage(.{
	.msg = try bundle.addString(fail_msg),
	});
	var cur_err: ?ErrorBundle.ErrorMessage = null;
	var cur_notes: std.ArrayList(ErrorBundle.ErrorMessage) = .empty;
	defer cur_notes.deinit(gpa);
	for (comp.diagnostics.output.to_list.messages.items) |msg| {
	switch (msg.kind) {
	// Clear the current error so that notes don't bleed into unassociated errors
	.off, .warning => {
	cur_err = null;
	continue;
	},
	.note => if (cur_err == null) continue,
	.@"fatal error", .@"error" => {},
	}
	const src_loc = src_loc: {
	if (msg.location) |location| {
	break :src_loc try bundle.addSourceLocation(.{
	.src_path = try bundle.addString(location.path),
	.line = location.line_no - 1, // 1-based -> 0-based
	.column = location.col - 1, // 1-based -> 0-based
	.span_start = location.width,
	.span_main = location.width,
	.span_end = location.width,
	.source_line = try bundle.addString(location.line),
	});
	}
	break :src_loc ErrorBundle.SourceLocationIndex.none;
	};
	switch (msg.kind) {
	.@"fatal error", .@"error" => {
	if (cur_err) |err| {
	try flushErrorMessageIntoBundle(&bundle, err, cur_notes.items);
	}
	cur_err = .{
	.msg = try bundle.addString(msg.text),
	.src_loc = src_loc,
	};
	cur_notes.clearRetainingCapacity();
	},
	.note => {
	cur_err.?.notes_len += 1;
	try cur_notes.append(gpa, .{
	.msg = try bundle.addString(msg.text),
	.src_loc = src_loc,
	});
	},
	.off, .warning => unreachable,
	}
	}
	if (cur_err) |err| {
	try flushErrorMessageIntoBundle(&bundle, err, cur_notes.items);
	}
	return try bundle.toOwnedBundle("");
	}