DebugInfo: Lazily built static member variable declarations should use the canonical declaration for line/file information.

When lazily constructing static member variable declarations (when
the vtable optimization fires and the definition of the type is omitted
(or built later, lazily), but the out of line definition of the static
member is provided and must be described in debug info) ensure we use
the canonical declaration when computing the file, line, etc for that
declaration (rather than the definition, which is also a declaration,
but not the canonical one).