Switch ARM back to libcorkscrew temporarily.

We're seeing major stack trace generation performance
regression and want to find out whether it's libunwind.

Bug: 12181612
Change-Id: I3866ea956859f5cbdfe4f1ee6f20a2b6d39962c4
diff --git a/libbacktrace/Android.mk b/libbacktrace/Android.mk
index eb55b47..a6b9c2b 100644
--- a/libbacktrace/Android.mk
+++ b/libbacktrace/Android.mk
@@ -22,8 +22,11 @@
 	libgccdemangle \
 	liblog \
 
-# To enable using libunwind on each arch, add it to the list below.
-ifeq ($(TARGET_ARCH),$(filter $(TARGET_ARCH),arm))
+# To enable using libunwind on each arch, add it to this list.
+libunwind_architectures :=
+#libunwind_architectures := arm
+
+ifeq ($(TARGET_ARCH),$(filter $(TARGET_ARCH),$(libunwind_architectures)))
 
 #----------------------------------------------------------------------------
 # The native libbacktrace library with libunwind.