Initial C++ runtime work. Much more to do.

runtime/atomic.h

@@ -0,0 +1,30 @@
+
+#ifndef __has_builtin
+#define __has_builtin(x) 0
+#endif
+#ifndef __has_feature
+#define __has_feature(x) 0
+#endif
+/**
+ * Swap macro that enforces a happens-before relationship with a corresponding
+ * ATOMIC_LOAD.
+ */
+#if __has_builtin(__c11_atomic_exchange)
+#define ATOMIC_SWAP(addr, val)\
+	__c11_atomic_exchange(reinterpret_cast<_Atomic(__typeof__(val))*>(addr), val, __ATOMIC_ACQ_REL)
+#elif __has_builtin(__sync_swap)
+#define ATOMIC_SWAP(addr, val)\
+	__sync_swap(addr, val)
+#else
+#define ATOMIC_SWAP(addr, val)\
+	__sync_lock_test_and_set(addr, val)
+#endif
+
+#if __has_builtin(__c11_atomic_load)
+#define ATOMIC_LOAD(addr)\
+	__c11_atomic_load(reinterpret_cast<_Atomic(__typeof__(*addr))*>(addr), __ATOMIC_ACQUIRE)
+#else
+#define ATOMIC_LOAD(addr)\
+	(__sync_synchronize(), *addr)
+#endif
+