DebugInfo: Don't emit a 'global variable' when a static member declaration is...

DebugInfo: Don't emit a 'global variable' when a static member declaration is referenced without a definition, just ensure the enclosing class (with the static member declaration) is emitted.

Addresses PR21511 by emitting appropriate metadata rather than
faux-global definitions for a variable that doesn't have a definition.

llvm-svn: 222377