atomic: Add include guards to the implementation headers

This makes them pass standalone compilation tests. Previously,
they included atomic.h which included themselves again, leading to
double definitions.

Signed-off-by: Martin Storsjö <martin@martin.st>

libavutil/atomic_gcc.h

@@ -18,6 +18,9 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+#ifndef AVUTIL_ATOMIC_GCC_H
+#define AVUTIL_ATOMIC_GCC_H
+
 #include "atomic.h"
 
 #define avpriv_atomic_int_get atomic_int_get_gcc
@@ -46,3 +49,5 @@ static inline void *atomic_ptr_cas_gcc(void * volatile *ptr,
 {
     return __sync_val_compare_and_swap(ptr, oldval, newval);
 }
+
+#endif /* AVUTIL_ATOMIC_GCC_H */

libavutil/atomic_suncc.h

@@ -17,6 +17,9 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+#ifndef AVUTIL_ATOMIC_SUNCC_H
+#define AVUTIL_ATOMIC_SUNCC_H
+
 #include <atomic.h>
 #include <mbarrier.h>
 
@@ -49,3 +52,4 @@ static inline void *atomic_ptr_cas_suncc(void * volatile *ptr,
     return atomic_cas_ptr(ptr, oldval, newval);
 }
 
+#endif /* AVUTIL_ATOMIC_SUNCC_H */

libavutil/atomic_win32.h

@@ -18,6 +18,9 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+#ifndef AVUTIL_ATOMIC_WIN32_H
+#define AVUTIL_ATOMIC_WIN32_H
+
 #include <windows.h>
 
 #include "atomic.h"
@@ -48,3 +51,5 @@ static inline void *atomic_ptr_cas_win32(void * volatile *ptr,
 {
     return InterlockedCompareExchangePointer(ptr, newval, oldval);
 }
+
+#endif /* AVUTIL_ATOMIC_WIN32_H */