DebugInfo: hoist definition into global context when needed

When generating debug info for a static inline member which is initialized for
the DLLExport storage class, hoist the definition into a non-composite type
context. Otherwise, we would trigger an assertion when generating the DIE for
the associated global value as the debug context has a type association. This
addresses PR22669.

Thanks to David Blakie for help in coming up with a solution to this!

llvm-svn: 230816