xf86atomic: #undef internal define

Thanks to the #error just above, any file including this header can only
see one state for this macro: defined, with the value `1`.
Let's just #undef it once we're done using it in here so that other
files don't misconstrue any meaning to it.

Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>

xf86atomic.h

@@ -101,6 +101,8 @@ typedef struct { LIBDRM_ATOMIC_TYPE atomic; } atomic_t;
 #error libdrm requires atomic operations, please define them for your CPU/compiler.
 #endif
 
+#undef HAS_ATOMIC_OPS
+
 static inline int atomic_add_unless(atomic_t *v, int add, int unless)
 {
 	int c, old;