ax__sync.m4: Include atomic.h for Solaris 10 test.

Author: wilx

configure

@@ -9695,6 +9695,7 @@ else
 /* end confdefs.h.  */
 
 #include <stdlib.h>
+#include <atomic.h>
 
 int
 main ()

m4/ax__sync.m4

@@ -188,6 +188,7 @@ AC_CACHE_CHECK([for atomic_dec_uint_nv], [ac_cv_atomic_dec_uint_nv],
     [AC_LANG_PROGRAM(
       [[
 #include <stdlib.h>
+#include <atomic.h>
       ]], 
       [[
 volatile unsigned int x = 2;