HLSL: Grammar: Make comma-separated declaration lists work.

Test/hlsl.init.frag

@@ -0,0 +1,12 @@
+float4 a1 = float4(1, 0.5, 0, 1), b1 = float4(2.0, 2.5, 2.1, 2.2);
+float a2 = 0.2, b2;
+float a3, b3 = 0.3;
+float a4, b4 = 0.4, c4;
+float a5 = 0.5, b5, c5 = 1.5;
+
+float4 ShaderFunction(float4 input) : COLOR0
+{
+    float4 a2 = float4(0.2, 0.3, 0.4, 0.5);
+
+    return input * a1;
+}