Add a test for writing to an indirect component of a vec4 TCS output

Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

tests/spec/arb_tessellation_shader/execution/variable-indexing/tcs-patch-vec4-index-wr.shader_test

+[require]
+GLSL >= 1.50
+GL_ARB_tessellation_shader
+
+[vertex shader]
+#version 150
+
+in vec4 piglit_vertex;
+
+void main()
+{
+    gl_Position = piglit_vertex;
+}
+
+[tessellation control shader]
+#version 150
+#extension GL_ARB_tessellation_shader : require
+layout(vertices = 4) out;
+
+uniform int index;
+patch out ivec4 v;
+
+void main()
+{
+    if (gl_InvocationID == 0)
+        v = ivec4(-1);
+
+    barrier();
+
+    v[gl_InvocationID] = int(gl_InvocationID);
+
+    gl_out[gl_InvocationID].gl_Position = gl_in[gl_InvocationID].gl_Position;
+    gl_TessLevelOuter = float[4](1.0, 1.0, 1.0, 1.0);
+    gl_TessLevelInner = float[2](1.0, 1.0);
+}
+
+[tessellation evaluation shader]
+#version 150
+#extension GL_ARB_tessellation_shader : require
+layout(quads, equal_spacing) in;
+
+uniform int index;
+patch in ivec4 v;
+out vec4 fscolor;
+
+#define INTERP_QUADj(INj, OUT) do { \
+    vec4 v[4]; \
+    for (int j = 0; j < 4; j++) v[j] = INj; \
+    OUT = mix(mix(v[0], v[1], gl_TessCoord[0]), mix(v[2], v[3], gl_TessCoord[0]), \
+              gl_TessCoord[1]); \
+} while(false)
+
+void main() {
+    bool pass = true;
+
+    for (int i = 0; i < 4; i++)
+        pass = pass && (v[i] == i);
+
+    fscolor = pass ? vec4(0.0, 1.0, 0.0, 1.0) : vec4(1.0, 0.0, 0.0, 1.0);
+
+    INTERP_QUADj(gl_in[j].gl_Position, gl_Position);
+}
+
+[fragment shader]
+#version 150
+in vec4 fscolor;
+out vec4 outcolor;
+
+void main()
+{
+    outcolor = fscolor;
+}
+
+[test]
+clear color 0.5 0.5 0.5 0.5
+clear
+
+patch parameter vertices 4
+
+draw rect patch -1 -1 0.09 0.09
+#draw arrays GL_PATCHES 0 4
+probe rgb 6 6 0.0 1.0 0.0