[5.1] IRGen: Map type into context before asking for class layout.

[jckarter]

Asking for the layout of the interface type apparently gives the wrong answer,
causing key paths to access stored properties of generic classes using the wrong
strategy.

Fixes SR-10167 | rdar://problem/49230751.

[jckarter]

@swift-ci Please test

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - f1a3673

[jckarter]

@swift-ci Please clean test Linux

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - f1a3673

[jckarter]

@swift-ci Please smoke test Linux

[jckarter]

@swift-ci Please test Linux

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - f1a3673

[jckarter]

@aciidb0mb3r My pr test has failed three times in a row here during swiftpm testing:

/home/buildnode/jenkins/workspace/swift-PR-Linux@2/branch-swift-5.1-branch/swiftpm/Tests/PackageDescription4Tests/VersionTests.swift:12:8: error: no such module 'XCTest'
import XCTest
       ^
--- bootstrap: erroe

Any known issues with swiftpm right now?

[aciidgh]

Could be related to swiftlang/swift-package-manager#2129
/cc @compnerd

[compnerd]

@aciidb0mb3r - that went into master, this is testing 5.1. Does the 5.1 branch use the master branch of swift-package-manager? If so, we need to pull that change into the 5.1 branch.

[compnerd]

Ugh! I see what happened; swift-corelibs-xctest merged from master into swift-5.1-branch but swift-package-manager did not. I will put up the PR for s-p-m in a minute

[compnerd]

Please test with following PRs:
swiftlang/swift-package-manager#2130

@swift-ci please test Linux platform