NCGenerics: fix runtime metadata request strategy (demangling vs response)

[kavon]

NCGenerics: fix runtime metadata request strategy

We generally should use the open-coded, metadata function "accessor"
strategy when targeting older runtimes, but if the type is part of
the stdlib, assume the runtime demangler will produce correct
metadata, as the retrofitting of Optional, etc, was done Carefully.

resolves rdar://131337585

---

NCGenerics: limit field metadata heuristic

We have had a heuristic that lets you reflect fields of types, where
the field's type is conditionally Copyable, despite the reflection
infrastructure always copying a field. That heuristic was added to allow
ubiquitous types like Optional in the stdlib to continue to be
reflected, even if the Optional at runtime really isn't Copyable.

As a consequence, we were also allowing reflection of fields containing
user-defined conditionally copyable types, when that's unsafe for no
real benefit, yielding runtime crashes!

I think in that case it's better to fall-back on the non-crashy case of
reflection seeing it as the EmptyTupleType, which isn't inhabited, so it
won't try to copy the field and instead basically skip-over it until a
future runtime supports the reflection safely.

So, this patch limits the dangerous reflection to only stdlib-defined
types, until Mirror and friends are updated.

[kavon]

@swift-ci test

[kavon]

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[kavon]

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[kavon]

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[kavon]

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[kavon]

@swift-ci smoke test macOS

[kavon]

@swift-ci smoke test macOS

[kavon]

@swift-ci smoke test macOS

[kavon]

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[kavon]

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[kavon]

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[kavon]

The only test that isn't passing still:

'Swift(iphonesimulator-x86_64) :: Interpreter/moveonly_reflection.swift'

An error was encountered processing the command (domain=NSPOSIXErrorDomain, code=2):
The operation couldn’t be completed. No such file or directory
No such file or directory

This appears to be some test-setup issue. My guess is the not binary isn't in the iphonesimulator.

[kavon]

@swift-ci smoke test