Update makefiles for host clang.

bug 16172793

Change-Id: If7484c5dbcccce7d925bec97bff0a3e4c30e9434
diff --git a/libbacktrace/Android.build.mk b/libbacktrace/Android.build.mk
index 2f55645..2685380 100644
--- a/libbacktrace/Android.build.mk
+++ b/libbacktrace/Android.build.mk
@@ -73,6 +73,7 @@
 ifeq ($(build_type),host)
   # Only build if host builds are supported.
   ifeq ($(build_host),true)
+    LOCAL_CFLAGS += -Wno-extern-c-compat
     ifneq ($($(module)_libc++),)
       include external/libcxx/libcxx.mk
     endif