Use libbacktrace instead of libcorkscrew.

Also, removed the ignore frames of 2, this was causing threads to chop
the lower two frames. The original code assumed that the calls to decode
the frame were in the unwind trace, but that's not the case.

Change-Id: Ifc0da0227f9114a5b462ef88e038439d58f951e9
diff --git a/runtime/Android.mk b/runtime/Android.mk
index 459ca0e..8df03cf 100644
--- a/runtime/Android.mk
+++ b/runtime/Android.mk
@@ -331,7 +331,7 @@
   endif
   LOCAL_C_INCLUDES += $(ART_C_INCLUDES)
   LOCAL_SHARED_LIBRARIES += liblog libnativehelper
-  LOCAL_SHARED_LIBRARIES += libcorkscrew # native stack trace support
+  LOCAL_SHARED_LIBRARIES += libbacktrace # native stack trace support
   ifeq ($$(art_target_or_host),target)
     LOCAL_SHARED_LIBRARIES += libcutils libz libdl libselinux
   else # host