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)

type.cpp

@@ -2448,6 +2448,8 @@ lCheckTypeEquality(const Type *a, const Type *b, bool ignoreConst) {
     if (sta != NULL && stb != NULL) {
         if (sta->GetElementCount() != stb->GetElementCount())
             return false;
+        if (sta->GetStructName() != stb->GetStructName())
+            return false;
         for (int i = 0; i < sta->GetElementCount(); ++i)
             if (!lCheckTypeEquality(sta->GetElementType(i), stb->GetElementType(i),
                                     ignoreConst))