tools/testing: add linux/args.h header and fix radix, VMA tests

Commit 857d18f23ab1 ("cleanup: Introduce ACQUIRE() and ACQUIRE_ERR() for
conditional locks") accidentally broke the radix tree, VMA userland tests
by including linux/args.h which is not present in the tools/include
directory.

This patch copies this over and adds an #ifdef block to avoid duplicate
__CONCAT declaration in conflict with system headers when we ultimately
include this.

Link: https://lkml.kernel.org/r/[e-mail]
Fixes: 857d18f23ab1 ("cleanup: Introduce ACQUIRE() and ACQUIRE_ERR() for conditional locks")
Signed-off-by: Lorenzo Stoakes <[e-mail]>
Cc: Jann Horn <[e-mail]>
Cc: John Hubbard <[e-mail]>
Cc: Liam Howlett <[e-mail]>
Cc: Sidhartha Kumar <[e-mail]>
Cc: Vlastimil Babka <[e-mail]>
Cc: Dan Williams <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

tools/include/linux/args.h

···
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _LINUX_ARGS_H
+#define _LINUX_ARGS_H
+
+/*
+ * How do these macros work?
+ *
+ * In __COUNT_ARGS() _0 to _12 are just placeholders from the start
+ * in order to make sure _n is positioned over the correct number
+ * from 12 to 0 (depending on X, which is a variadic argument list).
+ * They serve no purpose other than occupying a position. Since each
+ * macro parameter must have a distinct identifier, those identifiers
+ * are as good as any.
+ *
+ * In COUNT_ARGS() we use actual integers, so __COUNT_ARGS() returns
+ * that as _n.
+ */
+
+/* This counts to 15. Any more, it will return 16th argument. */
+#define __COUNT_ARGS(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, _n, X...) _n
+#define COUNT_ARGS(X...) __COUNT_ARGS(, ##X, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
+
+/* Concatenate two parameters, but allow them to be expanded beforehand. */
+#define __CONCAT(a, b) a ## b
+#define CONCATENATE(a, b) __CONCAT(a, b)
+
+#endif	/* _LINUX_ARGS_H */

tools/testing/shared/linux/idr.h

···
+/* Avoid duplicate definitions due to system headers. */
+#ifdef __CONCAT
+#undef __CONCAT
+#endif
 #include "../../../../include/linux/idr.h"