switch from __sync_add_and_fetch to __atomic_add_fetch

CHANGES

@@ -13,6 +13,7 @@ Notable User Facing Changes
   * and other small fixes and improvements
 - All device names used to control the platform setup via
   POCL_DEVICES are now lower case (as documented in the user manual).
+- Switch from __sync_*() to __atomic_*() (compiler builtins).
 
 3.0 June 2022
 =============

lib/CL/pocl_cl.h

@@ -77,9 +77,9 @@ typedef pthread_t pocl_thread_t;
 #if defined(__GNUC__) || defined(__clang__)
 
 /* These return the new value. */
-/* See: https://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/Atomic-Builtins.html */
-#define POCL_ATOMIC_INC(x) __sync_add_and_fetch (&x, 1)
-#define POCL_ATOMIC_DEC(x) __sync_sub_and_fetch (&x, 1)
+/* See: https://gcc.gnu.org/onlinedocs/gcc-4.7.4/gcc/_005f_005fatomic-Builtins.html */
+#define POCL_ATOMIC_INC(x) __atomic_add_fetch (&x, 1, __ATOMIC_SEQ_CST)
+#define POCL_ATOMIC_DEC(x) __atomic_sub_fetch (&x, 1, __ATOMIC_SEQ_CST)
 
 #elif defined(_WIN32)
 #define POCL_ATOMIC_INC(x) InterlockedIncrement64 (&x)