Enable -Wold-style-cast warnings for linker

  And fix old style casts.

Change-Id: I37e7a3e3fd852528ea76f02d967c7bd8cd5b06c9
diff --git a/linker/Android.mk b/linker/Android.mk
index e1302db..cc7fadf 100644
--- a/linker/Android.mk
+++ b/linker/Android.mk
@@ -35,6 +35,7 @@
 
 LOCAL_CPPFLAGS += \
     -std=gnu++11 \
+    -Wold-style-cast \
 
 ifeq ($(TARGET_IS_64_BIT),true)
 LOCAL_CPPFLAGS += -DTARGET_IS_64_BIT