Bump to WebRTC M120 release

Some API deprecation -- ExperimentalAgc and ExperimentalNs are gone.
We're continuing to carry iSAC even though it's gone upstream, but maybe
we'll want to drop that soon.

webrtc/rtc_base/system/no_unique_address.h

@@ -0,0 +1,37 @@
+/*
+ *  Copyright (c) 2020 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef RTC_BASE_SYSTEM_NO_UNIQUE_ADDRESS_H_
+#define RTC_BASE_SYSTEM_NO_UNIQUE_ADDRESS_H_
+
+// RTC_NO_UNIQUE_ADDRESS is a portable annotation to tell the compiler that
+// a data member need not have an address distinct from all other non-static
+// data members of its class.
+// It allows empty types to actually occupy zero bytes as class members,
+// instead of occupying at least one byte just so that they get their own
+// address. There is almost never any reason not to use it on class members
+// that could possibly be empty.
+// The macro expands to [[no_unique_address]] if the compiler supports the
+// attribute, it expands to nothing otherwise.
+// Clang should supports this attribute since C++11, while other compilers
+// should add support for it starting from C++20. Among clang compilers,
+// clang-cl doesn't support it yet and support is unclear also when the target
+// platform is iOS.
+#ifndef __has_cpp_attribute
+#define __has_cpp_attribute(x) 0
+#endif
+#if __has_cpp_attribute(no_unique_address)
+// NOLINTNEXTLINE(whitespace/braces)
+#define RTC_NO_UNIQUE_ADDRESS [[no_unique_address]]
+#else
+#define RTC_NO_UNIQUE_ADDRESS
+#endif
+
+#endif  // RTC_BASE_SYSTEM_NO_UNIQUE_ADDRESS_H_