Fix test case regressions on s390x arch

[rposts]

Code refactoring in Remote/MetadataReader.h resulted in RemoteAST test case failures on s390x architecture. Specifically, RemoteAST/structural_types.swift

Problems happens in MetadataRef readMetadata(StoredPointer address) method when a Tuple metadata is read. On s390x architecture, numElements, is returned correctly when its type is restored back to StoredSize.

[rposts]

@jckarter This commit changed the size of numElements - I suspect on BE systems using StoredSize makes more sense as the size is stored in high bytes - 93d8599#diff-517b9bd1bbb5b31cf61cd970872617ff

Let me know your thoughts. Thanks.

[compnerd]

Hmm, this technically changes the type, 32-bits to 64-bits. However, the TargetTupleTypeMetadata does store a StoredAddress for the NumElements. I think that the compiler enforced tuple element limit is preventing truncation, but, this seems generally correct. Thanks for fixing this!

[compnerd]

@swift-ci please test

[jckarter]

Yeah, this looks correct.

[rposts]

Thanks guys! Wonder if this can be merged in 5.0 branch or a separate PR is needed?

[jckarter]

Yeah, please start another PR for the swift 5.0 branch. It would need to be approved by the release managers.