Add 'EscapedFromIfConfig' bit to Decl

[bitjammer]

This is a temporary stop-gap for getting round-trip parsing
off the ground. The real fix, not re-injecting declarations
into an if-config's declaration context, is a deep dive and
is still ongoing.

[bitjammer]

@swift-ci Please smoke test

[bitjammer]

@DougGregor – are you ok with this temporary fix? I'm a bit stuck on conversions between operands of binary operators that I'll probably need your help with and I want to keep going getting round-trip printing up and running

[slavapestov]

I'll make you a deal. If you delete an equivalent number of lines of code from another file, you can merge this :-)

[CodaFi]

FWIW I have a branch looking at what I think the "deep dive" to fix this looks like. It ain't pretty, and it might cost us a pointer or two space in some AST nodes, but it gets the job done.

@DougGregor It would be helpful to know what parts of the ASTScope haven't been hammered out yet.

[bitjammer]

I don't believe you need to add any additional storage to stop leaking decls from if-configs.

[CodaFi]

Not under the current model. But to make this more dynamic (that is, to divest Parse of the responsibility) it has to be remodeled.

[DougGregor]

I'm okay with this, but of course I'd love to see @slavapestov 's code-deletion challenge met :)

[DougGregor]

@CodaFi ASTScope is still a bit broken, actually. It blows up still on some invalid code, mainly because the parser doesn't create sensible source ranges for broken code all the time. There might be some other oddities it doesn't handle well. I don't think it's hard to fix, but it just takes time to turn it on in stages and fix the breakage.

[bitjammer]

Thanks @DougGregor. I'll do my best to improve IfConfigDecl this week but I don't know if it will result in a net loss of LOC. I'll try to find some blank lines to sacrifice. ;-)