[dcl.init] No clear prohibition on initializing typedefs

[killerbee13]

Full name of submitter (unless configured in github; will be published with the issue): Bee

Reference (section label): [dcl.init], [dcl.decl.general]

Link to reflector thread (if any):

Issue description: There is no clear prohibition on the declaration typedef int x = 0; in [dcl.init], [dcl.decl.general], or in [dcl.typedef]. [dcl.init] assumes that there is a variable to initialize, but it isn't entirely clear if that constitutes a requirement or non-applicability.

Suggested resolution: Require in [dcl.init] or [dcl.decl.general] explicitly that an initializer shall only appear on an object declaration.

[t3nsor]

I think we may also be missing wording that says that in cases where an initializer is not permitted, the init-declarator is not checked for correctness as a default-initialization. This would apply to function declarations and non-defining variable declarations.