Use -Werror in frameworks/native/opengl/libagl

* Remove unused local variables and functions.

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: Ib8e3ee6e3c1ee3cf1e26f265fc87890f1690c6a2
diff --git a/opengl/libagl/Android.mk b/opengl/libagl/Android.mk
index c7635e2..15a12e4 100644
--- a/opengl/libagl/Android.mk
+++ b/opengl/libagl/Android.mk
@@ -38,6 +38,8 @@
 # The graphics code can generate division by zero
 LOCAL_CFLAGS_mips += -mno-check-zero-division
 
+LOCAL_CFLAGS += -Wall -Werror
+
 # we need to access the private Bionic header <bionic_tls.h>
 LOCAL_C_INCLUDES += bionic/libc/private