Put back inline definitions if using an old API.

All these inlines were turned in to out of line definitions in L.
This brings us a step closer to being able to just use the current
bionic headers for the NDK, rather than having many old versions of
them.

Change-Id: Ie010bc727d78d3742abc577c70f6578db2e68625
diff --git a/libc/include/android/legacy_sys_atomics_inlines.h b/libc/include/android/legacy_sys_atomics_inlines.h
new file mode 100644
index 0000000..85cbade
--- /dev/null
+++ b/libc/include/android/legacy_sys_atomics_inlines.h
@@ -0,0 +1,72 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifndef _ANDROID_LEGACY_SYS_ATOMICS_INLINES_H_
+#define _ANDROID_LEGACY_SYS_ATOMICS_INLINES_H_
+
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+/* Note: atomic operations that were exported by the C library didn't
+ *       provide any memory barriers, which created potential issues on
+ *       multi-core devices. We now define them as inlined calls to
+ *       GCC sync builtins, which always provide a full barrier.
+ *
+ *       NOTE: The C library still exports atomic functions by the same
+ *              name to ensure ABI stability for existing NDK machine code.
+ *
+ *       If you are an NDK developer, we encourage you to rebuild your
+ *       unmodified sources against this header as soon as possible.
+ */
+#define __ATOMIC_INLINE__ static __inline __attribute__((always_inline))
+
+__ATOMIC_INLINE__ int __atomic_cmpxchg(int old, int _new, volatile int *ptr) {
+  /* We must return 0 on success */
+  return __sync_val_compare_and_swap(ptr, old, _new) != old;
+}
+
+__ATOMIC_INLINE__ int __atomic_swap(int _new, volatile int *ptr) {
+  int prev;
+  do {
+    prev = *ptr;
+  } while (__sync_val_compare_and_swap(ptr, prev, _new) != prev);
+  return prev;
+}
+
+__ATOMIC_INLINE__ int __atomic_dec(volatile int *ptr) {
+  return __sync_fetch_and_sub(ptr, 1);
+}
+
+__ATOMIC_INLINE__ int __atomic_inc(volatile int *ptr) {
+  return __sync_fetch_and_add(ptr, 1);
+}
+
+__END_DECLS
+
+#endif /* _ANDROID_LEGACY_SYS_ATOMICS_INLINES_H_ */