selftests/vm/pkeys: make gcc check arguments of sigsafe_printf()

This will help us ensure we print pkey_reg_t values correctly in different
architectures.
Signed-off-by: Thiago Jung Bauermann <bauerman@linux.ibm.com>
Signed-off-by: Sandipan Das <sandipan@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Dave Hansen <dave.hansen@intel.com>
Cc: "Desnes A. Nunes do Rosario" <desnesn@linux.vnet.ibm.com>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Ram Pai <linuxram@us.ibm.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Suchanek <msuchanek@suse.de>
Cc: Shuah Khan <shuah@kernel.org>
Link: http://lkml.kernel.org/r/b40b7a95fdd4045d62530a2a34452934caf3b0bc.1585646528.git.sandipan@linux.ibm.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

tools/testing/selftests/vm/pkey-helpers.h

@@ -27,6 +27,10 @@
 #define DPRINT_IN_SIGNAL_BUF_SIZE 4096
 extern int dprint_in_signal;
 extern char dprint_in_signal_buffer[DPRINT_IN_SIGNAL_BUF_SIZE];
+
+#ifdef __GNUC__
+__attribute__((format(printf, 1, 2)))
+#endif
 static inline void sigsafe_printf(const char *format, ...)
 {
 	va_list ap;