selftests/mm: centralize the __always_unused macro

This macro gets used in different tests. Add it to kselftest.h which is
central location and tests use this header. Then use this new macro.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Muhammad Usama Anjum <[e-mail]>
Acked-by: David Hildenbrand <[e-mail]>
Cc: Antonio Quartulli <[e-mail]>
Cc: David S. Miller <[e-mail]>
Cc: Eric Dumazet <[e-mail]>
Cc: Jakub Kacinski <[e-mail]>
Cc: Liam Howlett <[e-mail]>
Cc: Lorenzo Stoakes <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Mike Rapoport <[e-mail]>
Cc: Paolo Abeni <[e-mail]>
Cc: "Sabrina Dubroca" <[e-mail]>
Cc: Shuah Khan <[e-mail]>
Cc: Simon Horman <[e-mail]>
Cc: Suren Baghdasaryan <[e-mail]>
Cc: Vlastimil Babka <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

tools/testing/selftests/kselftest.h

···
 #endif
 #define __printf(a, b)   __attribute__((format(printf, a, b)))
 
+#ifndef __always_unused
+#define __always_unused __attribute__((__unused__))
+#endif
+
 #ifndef __maybe_unused
 #define __maybe_unused __attribute__((__unused__))
 #endif

tools/testing/selftests/mm/protection_keys.c

···
 
 static void test_ptrace_of_child(int *ptr, u16 pkey)
 {
-	__attribute__((__unused__)) int peek_result;
+	__always_unused int peek_result;
 	pid_t child_pid;
 	void *ignored = 0;
 	long ret;

tools/testing/selftests/net/ovpn/ovpn-cli.c

···
 
 #include <sys/socket.h>
 
+#include "../../kselftest.h"
+
 /* defines to make checkpatch happy */
 #define strscpy strncpy
-#define __always_unused __attribute__((__unused__))
 
 /* libnl < 3.5.0 does not set the NLA_F_NESTED on its own, therefore we
  * have to explicitly do it to prevent the kernel from failing upon