SPV: Fix issue #159: use ExplicitLod forms for non-fragment stages.

Test/spv.150.vert

@@ -4,6 +4,7 @@ in vec4 iv4;
 
 uniform float ps;
 uniform int ui;
+uniform sampler2D s2D;
 
 invariant gl_Position;
 
@@ -27,13 +28,11 @@ void main()
     gl_ClipDistance[2] = iv4.x;
     int i;
     s2out.d[i].b[2].w = ps;
-    
-    // test recovery from nonsupported built-ins    
-    //float n1 = noise1(2.4);
-    //n1 = noise1(vec4(n1));
-    //vec2 n2 = noise2(vec3(n1));
-    //vec3 n3 = noise3(n2);
-    //vec4 n4 = noise4(n3);
+
+    // test non-implicit lod
+    texture(s2D, vec2(0.5));
+    textureProj(s2D, vec3(0.5));
+    textureLod(s2D, vec2(0.5), 3.2);
 }
 
 out float gl_ClipDistance[4];