GLSL front-end: Check recursively for opaque types in a block; these are all illegal.

glslang/Include/Types.h

@@ -1161,6 +1161,19 @@ public:
         return false;
     }
 
+    virtual bool containsOpaque() const
+    {
+        if (basicType == EbtSampler || basicType == EbtAtomicUint)
+            return true;
+        if (! structure)
+            return false;
+        for (unsigned int i = 0; i < structure->size(); ++i) {
+            if ((*structure)[i].type->containsOpaque())
+                return true;
+        }
+        return false;
+    }
+
     // Array editing methods.  Array descriptors can be shared across
     // type instances.  This allows all uses of the same array
     // to be updated at once.  E.g., all nodes can be explicitly sized