[Foundation] Reorder _DataStorage to save 14 bytes of overhead

[phausler]

The backing storage for Data (_DataStorage) previously would require an allocation size of 72 bytes for the overs, however re-ordering the members to a more compact layout can easily yield considerably less. We can shave off 14 bytes and hit a mark of 58 bytes per storage for the ivars; which can easily fit into a smaller bucket size (not accounting for the class information).

This resolves the following issues:
rdar://problem/38150740

[phausler]

@swift-ci please test

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - aae9601

[phausler]

@swift-ci please clean test

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - aae9601

[phausler]

@swift-ci please test Linux

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - aae9601

[phausler]

The failure listed has nothing to do with Data itself from what I can tell.

[jrose-apple]

I hit it too. @aciidb0mb3r, know what's up with llbuild?

[aciidgh]

Dunno, this seems new. /cc @ddunbar

[jrose-apple]

We've been messing with the driver, so it could be our side too. Weird that it's not hitting the regular builders, though.

[aciidgh]

I did change llbuild to build in release mode, maybe that is somehow related.

[ddunbar]

@Aciid maybe related to change to build in release mode? Should we revert?

[jrose-apple]

Ah, yes, that would do it. You turned on -O and -wmo but didn't pass -num-threads, so it assumed you wanted a single object file in the current directory instead of respecting the output file map. And I believe we can't warn about this because Xcode always provides the same output file map for both WMO and non-WMO builds.

[aciidgh]

Reproduces locally if I try to build bindings. Reverting..

[aciidgh]

Raised this to disable release mode when building bindings swiftlang/swift-llbuild#233

[phausler]

Thanks for the help hunting down this failure.

@swift-ci please smoke test

[phausler]

@swift-ci please smoke test macOS

[parkera]

@swift-ci please smoke test macOS

[phausler]

@swift-ci please smoke test macOS

[phausler]

@shahmishal do you know what is going on here? it does not seem to be responding to me. this has been outstanding for a long while and id like to eventually get this landed.

[jrose-apple]

It smoke tested successfully. It's the full test that hasn't updated (and won't), but that's not strictly blocking you from merging.

[CodaFi]

Superseded by #28327