Missing Variable Declaration in the Lookup Table

[kumarak]

The variable declaration may be missing in the Lookup Table while lowering the DeclRefExpr. I found a few instances of this issue with file-scoped variables and variables having non-ODR references while lowering the translation unit

Raised a PR #383 to find such cases and emit error. But it should be fixed by investigating the issue or visiting the decl node before lowering DeclRefExpr if it has not been before.