Provide a real feature test for __attribute__().

Looking at version numbers like __GNUC__ is always a bad idea.
Believe it or not, this even makes ./configure shorter by one line.

1 files changed, 48 insertions, 0 deletions

diff --git a/test-attribute.c b/test-attribute.c
new file mode 100644
index 00000000..adbcc926
--- /dev/null
+++ b/test-attribute.c
@@ -0,0 +1,48 @@
+/* $Id: test-attribute.c,v 1.1 2020/06/22 20:00:38 schwarze Exp $ */
+/*
+ * Copyright (c) 2020 Ingo Schwarze <schwarze@openbsd.org>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+void	 var_arg(const char *, ...)
+		__attribute__((__format__ (__printf__, 1, 2)));
+void	 no_ret(int)
+		__attribute__((__noreturn__));
+
+void
+var_arg(const char *fmt, ...)
+{
+	va_list	 ap;
+
+	va_start(ap, fmt);
+	vprintf(fmt, ap);
+	va_end(ap);
+}
+
+void
+no_ret(int i)
+{
+	exit(i);
+}
+
+int
+main(void)
+{
+	var_arg("Test output: %d\n", 42);
+	no_ret(0);
+}