Assertion in clang when referring to a structure type that doesn't exist

Trying to compile the following code:

```
kernel void test(global struct nope* arg) {}
```

leads to the following assertion

```
clspv: clspv/third_party/clang/lib/AST/RecordLayoutBuilder.cpp:2987: const clang::ASTRecordLayout& clang::ASTContext::getASTRecordLayout(const clang::RecordDecl*) const: Assertion `D && "Cannot get layout of forward declarations!"' failed.
Abandon
```