Link: Merge all the settings in TIntermediate.

Fixes #1309.

glslang/Include/Types.h

@@ -616,6 +616,22 @@ public:
         }
     }
 
+    // non-built-in symbols that might link between compilation units
+    bool isLinkable() const
+    {
+        switch (storage) {
+        case EvqGlobal:
+        case EvqVaryingIn:
+        case EvqVaryingOut:
+        case EvqUniform:
+        case EvqBuffer:
+        case EvqShared:
+            return true;
+        default:
+            return false;
+        }
+    }
+
     // True if this type of IO is supposed to be arrayed with extra level for per-vertex data
     bool isArrayedIo(EShLanguage language) const
     {