Link libunwind_llvm to the ASan runtime library.

This fixes stack unwind in ASan reports broken by LOCAL_CXX_STL := none change.
That change resulted in ASan using the libgcc unwinder, parts of which are interposed
by similarly-named functions from libc++abi re-exported by all platform executables.

Change-Id: I904603fdc5fda8554283cd43a9e0c0a2e22be93d
diff --git a/lib/asan/Android.mk b/lib/asan/Android.mk
index 8e69ae3..92565a2 100644
--- a/lib/asan/Android.mk
+++ b/lib/asan/Android.mk
@@ -158,6 +158,8 @@
 LOCAL_CPP_EXTENSION := .cc
 LOCAL_SHARED_LIBRARIES := liblog libc libdl
 LOCAL_STATIC_LIBRARIES := libcompiler_rt libubsan
+LOCAL_STATIC_LIBRARIES_arm := libunwind_llvm
+LOCAL_LDFLAGS_arm := -Wl,--exclude-libs,libunwind_llvm.a
 # MacOS toolchain is out-of-date and does not support -z global.
 # TODO: re-enable once the toolchain issue is fixed.
 ifneq ($(HOST_OS),darwin)