[SR-15044] Module caching is not working with SDK frameworks in the test suite

[typesanitizer]

Previous ID	SR-15044
Radar	rdar://problem/81672238
Original Reporter	@typesanitizer
Type	Bug

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug
Assignee	None
Priority	Medium

md5: d9ed259c9a6c3b3c108979d1c6a2d7b8

relates to:

• SR-15043 Prune needless dependencies on the real Foundation

Issue Description:

Consider a basic test like below:

// RUN: %target-swift-frontend %s -typecheck -verify
import Foundation

This takes 15+ seconds every time with a ReleaseAssert compiler. This seems to indicate the module caching is not working. Instead, it looks like the cache is being blown away and a new cache is being created (cue infinite scream) – I checked this by repeatedly running cd ~ && cd - && ls in the cache directory while the test was running and seeing swiftmodule files being regenerated.

We should fix this to reduce test times.

[typesanitizer]

@swift-ci create

[typesanitizer]

PR #38806