clang: pacify clang wrt ompi use of c11 atomics

The clang compiler (or at least the one used by the Cray CCE 9 and newer)
doesn't like what we're doing passing non _Atomic pointers to C11 atomics.
Fix the ones that keep vader from compiling using Cray CCE 9 and 10.

Signed-off-by: Howard Pritchard <howardp@lanl.gov>

opal/include/opal/sys/atomic_stdc.h

@@ -5,6 +5,8 @@
  * Copyright (c) 2018      Research Organization for Information Science
  *                         and Technology (RIST).  All rights reserved.
  * Copyright (c) 2019      Google, LLC. All rights reserved.
+ * Copyright (c) 2019      Triad National Security, LLC. All rights
+ *                         reserved.
  * $COPYRIGHT$
  *
  * Additional copyrights may follow
@@ -99,9 +101,9 @@ static inline void opal_atomic_rmb (void)
 #define opal_atomic_compare_exchange_strong_acq(addr, oldval, newval)  atomic_compare_exchange_strong_explicit (addr, oldval, newval, memory_order_acquire, memory_order_relaxed)
 #define opal_atomic_compare_exchange_strong_rel(addr, oldval, newval)  atomic_compare_exchange_strong_explicit (addr, oldval, newval, memory_order_release, memory_order_relaxed)
 
-#define opal_atomic_swap_32(addr, value) atomic_exchange_explicit (addr, value, memory_order_relaxed)
-#define opal_atomic_swap_64(addr, value) atomic_exchange_explicit (addr, value, memory_order_relaxed)
-#define opal_atomic_swap_ptr(addr, value) atomic_exchange_explicit (addr, value, memory_order_relaxed)
+#define opal_atomic_swap_32(addr, value) atomic_exchange_explicit ((_Atomic unsigned int *)addr, value, memory_order_relaxed)
+#define opal_atomic_swap_64(addr, value) atomic_exchange_explicit ((_Atomic unsigned long *)addr, value, memory_order_relaxed)
+#define opal_atomic_swap_ptr(addr, value) atomic_exchange_explicit ((_Atomic unsigned long *)addr, value, memory_order_relaxed)
 
 #define OPAL_ATOMIC_STDC_DEFINE_FETCH_OP(op, bits, type, operator)      \
     static inline type opal_atomic_fetch_ ## op ##_## bits (opal_atomic_ ## type *addr, type value) \