Atomic_GCC: Throw out old code

Source/Core/Common/Atomic_GCC.h

@@ -50,19 +50,6 @@ inline void AtomicOr(volatile u32& target, u32 value)
 	__sync_or_and_fetch(&target, value);
 }
 
-// Support clang versions older than 3.4.
-#if __clang__ && !__has_feature(cxx_atomic)
-template <typename T>
-_Atomic(T)* ToC11Atomic(volatile T* loc)
-{
-	return (_Atomic(T)*) loc;
-}
-
-#define __atomic_load_n(p, m) __c11_atomic_load(ToC11Atomic(p), m)
-#define __atomic_store_n(p, v, m) __c11_atomic_store(ToC11Atomic(p), v, m)
-#define __atomic_exchange_n(p, v, m) __c11_atomic_exchange(ToC11Atomic(p), v, m)
-#endif
-
 #ifndef __ATOMIC_RELAXED
 #error __ATOMIC_RELAXED not defined; your compiler version is too old.
 #endif

Source/Core/Common/Common.h

@@ -8,10 +8,6 @@
 #include <cstdlib>
 #include <cstring>
 
-#ifndef __has_feature
-#define __has_feature(x) 0
-#endif
-
 // Git version number
 extern const char *scm_desc_str;
 extern const char *scm_branch_str;