Add link-time cross stage optimization test

Test/link.crossStageOptimization.vert

@@ -0,0 +1,41 @@
+#version 440
+
+layout(std140) uniform AccessedUniformBlock
+{
+    vec4 a;
+    vec4 b;
+};
+
+layout(std140) uniform NotAccessedUniformBlock
+{
+    vec4 c;
+    vec4 d;
+};
+
+layout(std430) buffer AccessedStorageBlock
+{
+    float e[512];
+};
+
+layout(std430) buffer NotAccessedStorageBlock
+{
+    float f[512];
+};
+
+uniform sampler2D uSampler0; // accessed
+uniform sampler2D uSampler1; // not accessed
+
+layout(location = 0) out vec4 a0; // accessed
+layout(location = 1) out vec4 a1; // not accessed
+layout(location = 2) out vec4 a2; // accessed
+layout(location = 3) out vec4 a3; // not accessed
+
+void main()
+{
+    a0 = a + vec4(e[0]) + texture(uSampler0, vec2(0.5, 0.5));
+    a1 = c + vec4(f[1]) + texture(uSampler1, vec2(0.5, 0.5));
+    a2 = b + vec4(e[0]) + texture(uSampler0, vec2(0.5, 0.5));
+    a3 = d + vec4(f[1]) + texture(uSampler1, vec2(0.5, 0.5));
+
+    gl_Position = vec4(1.0, 1.0, 1.0, 1.0);
+}