kselftest/arm64: Use shared OPTIMZER_HIDE_VAR() definiton

We had open coded the definition of OPTIMIZER_HIDE_VAR() as a fix but now
that we have the generic tools/include available and that has had a
definition of OPTIMIZER_HIDE_VAR() we can switch to the define.
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20230728-arm64-signal-memcpy-fix-v4-5-0c1290db5d46@kernel.orgSigned-off-by: Will Deacon <will@kernel.org>

tools/testing/selftests/arm64/signal/test_signals_utils.h

@@ -8,6 +8,8 @@
 #include <stdio.h>
 #include <string.h>
 
+#include <linux/compiler.h>
+
 #include "test_signals.h"
 
 int test_init(struct tdescr *td);
@@ -76,7 +78,7 @@ static __always_inline bool get_current_context(struct tdescr *td,
 	 */
 	for (i = 0; i < td->live_sz; i++) {
 		uc[i] = 0;
-		__asm__ ("" : "=r" (uc[i]) : "0" (uc[i]));
+		OPTIMIZER_HIDE_VAR(uc[0]);
 	}
 
 	td->live_uc = dest_uc;