fix regression disabling use of pause instruction for x86 a_spin

commits e24984efd5 and
16b55298dc inadvertently disabled the
a_spin implementations for i386, x86_64, and x32 by defining a macro
named a_pause instead of a_spin. this should not have caused any
functional regression, but it inhibited cpu relaxation while spinning
for locks.

bug reported by George Kulakowski.

arch/i386/atomic_arch.h

@@ -71,7 +71,7 @@ static inline void a_barrier()
 	__asm__ __volatile__( "" : : : "memory" );
 }
 
-#define a_pause a_pause
+#define a_spin a_spin
 static inline void a_spin()
 {
 	__asm__ __volatile__( "pause" : : : "memory" );

arch/x32/atomic_arch.h

@@ -87,7 +87,7 @@ static inline void a_barrier()
 	__asm__ __volatile__( "" : : : "memory" );
 }
 
-#define a_pause a_pause
+#define a_spin a_spin
 static inline void a_spin()
 {
 	__asm__ __volatile__( "pause" : : : "memory" );

arch/x86_64/atomic_arch.h

@@ -96,7 +96,7 @@ static inline void a_barrier()
 	__asm__ __volatile__( "" : : : "memory" );
 }
 
-#define a_pause a_pause
+#define a_spin a_spin
 static inline void a_spin()
 {
 	__asm__ __volatile__( "pause" : : : "memory" );