Revert "lavu/atomic: add support for the new memory model aware gcc built-ins"

This reverts commit faa9d298.

This change became superfluous when support for C11 atomics was introduced.
Reverting it will make the removal of this implementation in an upcoming
merge conflict free.
Reviewed-by: wm4 <nfxjfg@googlemail.com>
Signed-off-by: James Almer <jamrial@gmail.com>

configure

@@ -1821,7 +1821,6 @@ ARCH_FEATURES="
 
 BUILTIN_LIST="
     atomic_cas_ptr
-    atomic_compare_exchange
     machine_rw_barrier
     MemoryBarrier
     mm_empty
@@ -2322,7 +2321,7 @@ symver_if_any="symver_asm_label symver_gnu_asm"
 valgrind_backtrace_deps="!optimizations valgrind_valgrind_h"
 
 # threading support
-atomics_gcc_if_any="sync_val_compare_and_swap atomic_compare_exchange"
+atomics_gcc_if="sync_val_compare_and_swap"
 atomics_suncc_if="atomic_cas_ptr machine_rw_barrier"
 atomics_win32_if="MemoryBarrier"
 atomics_native_if_any="$ATOMICS_LIST"
@@ -5533,7 +5532,6 @@ if ! disabled network; then
 fi
 
 check_builtin atomic_cas_ptr atomic.h "void **ptr; void *oldval, *newval; atomic_cas_ptr(ptr, oldval, newval)"
-check_builtin atomic_compare_exchange "" "int *ptr, *oldval; int newval; __atomic_compare_exchange_n(ptr, oldval, newval, 0, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST)"
 check_builtin machine_rw_barrier mbarrier.h "__machine_rw_barrier()"
 check_builtin MemoryBarrier windows.h "MemoryBarrier()"
 check_builtin sarestart signal.h "SA_RESTART"

libavutil/atomic_gcc.h

@@ -28,40 +28,27 @@
 #define avpriv_atomic_int_get atomic_int_get_gcc
 static inline int atomic_int_get_gcc(volatile int *ptr)
 {
-#if HAVE_ATOMIC_COMPARE_EXCHANGE
-    return __atomic_load_n(ptr, __ATOMIC_SEQ_CST);
-#else
     __sync_synchronize();
     return *ptr;
-#endif
 }
 
 #define avpriv_atomic_int_set atomic_int_set_gcc
 static inline void atomic_int_set_gcc(volatile int *ptr, int val)
 {
-#if HAVE_ATOMIC_COMPARE_EXCHANGE
-    __atomic_store_n(ptr, val, __ATOMIC_SEQ_CST);
-#else
     *ptr = val;
     __sync_synchronize();
-#endif
 }
 
 #define avpriv_atomic_int_add_and_fetch atomic_int_add_and_fetch_gcc
 static inline int atomic_int_add_and_fetch_gcc(volatile int *ptr, int inc)
 {
-#if HAVE_ATOMIC_COMPARE_EXCHANGE
-    return __atomic_add_fetch(ptr, inc, __ATOMIC_SEQ_CST);
-#else
     return __sync_add_and_fetch(ptr, inc);
-#endif
 }
 
 #define avpriv_atomic_ptr_cas atomic_ptr_cas_gcc
 static inline void *atomic_ptr_cas_gcc(void * volatile *ptr,
                                        void *oldval, void *newval)
 {
-#if HAVE_SYNC_VAL_COMPARE_AND_SWAP
 #ifdef __ARMCC_VERSION
     // armcc will throw an error if ptr is not an integer type
     volatile uintptr_t *tmp = (volatile uintptr_t*)ptr;
@@ -69,10 +56,6 @@ static inline void *atomic_ptr_cas_gcc(void * volatile *ptr,
 #else
     return __sync_val_compare_and_swap(ptr, oldval, newval);
 #endif
-#else
-    __atomic_compare_exchange_n(ptr, &oldval, newval, 0, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST);
-    return oldval;
-#endif
 }
 
 #endif /* AVUTIL_ATOMIC_GCC_H */