Ensure that both parameter lists are the same length in function overloading.

Fixes new test function-05.glsl, where the second function has matching
parameter types, but less of them.

tests/function-05.glsl

@@ -0,0 +1,26 @@
+/* PASS */
+
+vec4 foo(in float x, in float y, float z, float w)
+{
+  vec4 v;
+  v.x = x;
+  v.y = y;
+  v.z = z;
+  v.w = w;
+  return v;
+}
+
+vec4 foo(in float x)
+{
+   vec4 v;
+   v.x = x;
+   v.y = x;
+   v.z = x;
+   v.w = x;
+}
+
+void main()
+{
+  gl_Position = foo(1.0, 1.0, 1.0, 0.0);
+  gl_Position = foo(2.0);
+}