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/primitives.cpp b/opengl/libagl/primitives.cpp
index 57a798d..d3b19e8 100644
--- a/opengl/libagl/primitives.cpp
+++ b/opengl/libagl/primitives.cpp
@@ -241,6 +241,7 @@
     m_dx20 = v0->window.x - v2->window.x;
     m_dy02 = v2->window.y - v0->window.y;
     m_area = m_dx01*m_dy02 + (-m_dy10)*m_dx20;
+    (void)m_reserved; // suppress unused warning
 }
 
 void compute_iterators_t::initLine(