Add arm64 to typedefs.h

This is the first step to get a buildable chrome_shell_apk for arm64.

BUG=chromium:354405
R=andrew@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/10819004

Patch from Primiano Tucci <primiano@chromium.org>.

git-svn-id: http://webrtc.googlecode.com/svn/trunk@5802 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/webrtc/typedefs.h b/webrtc/typedefs.h
index 4857908..09e30d2 100644
--- a/webrtc/typedefs.h
+++ b/webrtc/typedefs.h
@@ -23,6 +23,9 @@
 #define WEBRTC_ARCH_X86_64
 #define WEBRTC_ARCH_64_BITS
 #define WEBRTC_ARCH_LITTLE_ENDIAN
+#elif defined(__arm64__) || defined(__aarch64__)
+#define WEBRTC_ARCH_64_BITS
+#define WEBRTC_ARCH_LITTLE_ENDIAN
 #elif defined(_M_IX86) || defined(__i386__)
 #define WEBRTC_ARCH_X86_FAMILY
 #define WEBRTC_ARCH_X86
@@ -44,7 +47,6 @@
 #elif defined(__pnacl__)
 #define WEBRTC_ARCH_32_BITS
 #define WEBRTC_ARCH_LITTLE_ENDIAN
-#define WEBRTC_LITTLE_ENDIAN
 #else
 #error Please add support for your architecture in typedefs.h
 #endif