Toolbox: Disable unused-const-variable warning

For build-system CFLAGS clean-up, disable unused-const-variable
warning.

Bug: 18632512
Change-Id: I1be1ac744f8c77bd0a8378578072285a2c035245
diff --git a/toolbox/Android.mk b/toolbox/Android.mk
index 273b263..aa92af7 100644
--- a/toolbox/Android.mk
+++ b/toolbox/Android.mk
@@ -2,7 +2,7 @@
 
 
 common_cflags := \
-    -Werror -Wno-unused-parameter \
+    -Werror -Wno-unused-parameter -Wno-unused-const-variable \
     -I$(LOCAL_PATH)/upstream-netbsd/include/ \
     -include bsd-compatibility.h \