Get arm64 to compile.

Change-Id: Ica021aa134388fe7069a5de5df8036ecf0d570f8

libbacktrace/Android.mk

@@ -23,8 +23,7 @@ common_shared_libs := \
 	liblog \
 
 # To enable using libunwind on each arch, add it to this list.
-libunwind_architectures :=
-#libunwind_architectures := arm
+libunwind_architectures := arm64
 
 ifeq ($(TARGET_ARCH),$(filter $(TARGET_ARCH),$(libunwind_architectures)))
 

libbacktrace/UnwindCurrent.cpp

@@ -43,7 +43,7 @@
   #include <asm/sigcontext.h>
   #include <asm/ucontext.h>
   typedef struct ucontext ucontext_t;
-#elif !defined(__mips__)
+#elif !defined(__mips__) && !defined(__aarch64__)
   #error Unsupported architecture.
 #endif