Add -Wno-deprecated-register to handle external/freetype.

Bug: 17163086
Change-Id: I3f646f8e0ce06dec14895accf3225de7ac95a9c3
diff --git a/Android.mk b/Android.mk
index 5e4f82e..98ff0a6 100644
--- a/Android.mk
+++ b/Android.mk
@@ -176,6 +176,9 @@
 LOCAL_C_INCLUDES += external/libcxx/include
 
 LOCAL_CFLAGS += $(rs_base_CFLAGS)
+# TODO: external/freetype still uses the register keyword
+# Bug: 17163086
+LOCAL_CFLAGS += -Wno-deprecated-register
 
 LOCAL_CPPFLAGS += -fno-exceptions