Documentation/litmus-tests: Make cmpxchg() tests safe for klitmus

The four litmus tests in Documentation/litmus-tests/atomic do not
declare all of their local variables.  Although this is just fine for LKMM
analysis by herd7, it causes build failures when run in-kernel by klitmus.
This commit therefore adjusts these tests to declare all local variables.
Reported-by: Andrea Parri <parri.andrea@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Acked-by: Andrea Parri <parri.andrea@gmail.com>

Documentation/litmus-tests/atomic/cmpxchg-fail-ordered-1.litmus

@@ -23,6 +23,7 @@ P0(int *x, int *y, int *z)
 P1(int *x, int *y, int *z)
 {
 	int r0;
+	int r1;
 
 	WRITE_ONCE(*y, 1);
 	r1 = cmpxchg(z, 1, 0);

Documentation/litmus-tests/atomic/cmpxchg-fail-ordered-2.litmus

@@ -11,7 +11,6 @@ C cmpxchg-fail-ordered-2
 
 P0(int *x, int *y)
 {
-	int r0;
 	int r1;
 
 	WRITE_ONCE(*x, 1);
@@ -20,7 +19,8 @@ P0(int *x, int *y)
 
 P1(int *x, int *y)
 {
-	int r0;
+	int r1;
+	int r2;
 
 	r1 = cmpxchg(y, 0, 1);
 	smp_mb__after_atomic();

Documentation/litmus-tests/atomic/cmpxchg-fail-unordered-1.litmus

@@ -23,6 +23,7 @@ P0(int *x, int *y, int *z)
 P1(int *x, int *y, int *z)
 {
 	int r0;
+	int r1;
 
 	WRITE_ONCE(*y, 1);
 	r1 = cmpxchg(z, 1, 0);

Documentation/litmus-tests/atomic/cmpxchg-fail-unordered-2.litmus

@@ -12,7 +12,6 @@ C cmpxchg-fail-unordered-2
 
 P0(int *x, int *y)
 {
-	int r0;
 	int r1;
 
 	WRITE_ONCE(*x, 1);
@@ -21,7 +20,8 @@ P0(int *x, int *y)
 
 P1(int *x, int *y)
 {
-	int r0;
+	int r1;
+	int r2;
 
 	r1 = cmpxchg(y, 0, 1);
 	r2 = READ_ONCE(*x);