We were (unintentionally) only using structural equivalence to compare struct types.

Now we require that the struct name match for two struct types to be the same.
Added a test to check this.
(Also removed a stale test, movmsk-opt.ispc)

tests/movmsk-opt.ispc

@@ -1,35 +0,0 @@
-static float float4(uniform float a, uniform float b, uniform float c, 
-                    uniform float d) {
-    float ret = 0;
-    for (uniform int i = 0; i < programCount; i += 4) {
-        ret = insert(ret, i + 0, a);
-        ret = insert(ret, i + 1, b);
-        ret = insert(ret, i + 2, c);
-        ret = insert(ret, i + 3, d);
-    }
-    return ret;
-}
-
-export uniform int width() { return programCount; }
-
-
-
-export void f_fu(uniform float RET[], uniform float aFOO[], uniform float b) {
-    float a = aFOO[programIndex];
-    uniform int ret = 0;
-
-    float v = float4(1,1,0,0);
-    bool b = (v == 1.);
-    ret = __movmsk((sign_extend(b)));
-    RET[programIndex] = ret;
-}
-
-
-// fixme for 16-wide...
-export void result(uniform float RET[]) { 
-    uniform int x = -1234;
-    if (programCount == 4) x = 3;
-    else if (programCount == 8) x = 0x33;
-    else if (programCount == 16) x = 0x3333;
-    RET[programIndex] = x;
-}