older Swift versions installed via Swiftly don’t work with `swift build` or Xcode

[Skoti]

I've downloaded a few Swift versions through swiftly but I'm encountering issues when trying to build through Xcode or with swift build.

Swift Version	swift build	Xcode Version 16.4 (16F6)	Issue
6.2.0	✅	✅
6.1.2	✅	✅
6.0.3	✅	✅
6.0.0	💥	💥	crash during SIL deserialization - see below for details
5.10.0	❌	❌	error: could not build module 'DarwinFoundation' and some others
5.9.2	❌	❌	swift build   error: invalid tool type in 'tools' map   error: unable to load build file Xcode   error: could not build module 'DarwinFoundation' and some others

6.0 crash

1.	Apple Swift version 6.0 (swift-6.0-RELEASE)
2.	Compiling with effective version 5.10
3.	While evaluating request ExecuteSILPipelineRequest(Run pipelines { Mandatory Diagnostic Passes + Enabling Optimization Passes } on SIL for Darwin)
4.	While running pass #2548 SILModuleTransform "MandatorySILLinker".
5.	While deserializing SIL function "$s6Darwin14POSIXErrorCodeO8rawValueACSgs5Int32V_tcfC"
6.	*** DESERIALIZATION FAILURE ***
*** If any module named here was modified in the SDK, please delete the ***
*** new swiftmodule files from the SDK and keep only swiftinterfaces.   ***
module '_errno', builder version '6.0(6.0)/Apple Swift version 6.0 (swift-6.0-RELEASE)', built from swiftinterface, resilient, loaded from '/var/folders/3n/h4h_m9zx25z1nm5l0ns5xzzm0000gn/C/clang/ModuleCache/_errno-2X4MHLH8U7AYI.swiftmodule'
SILFunction type mismatch for '$s6Darwin14POSIXErrorCodeO8rawValueACSgs5Int32V_tcfC': '$@convention(method) (Int32, @thin POSIXErrorCode.Type) -> Optional<POSIXErrorCode>' != '$@convention(method) (Int32, @thin POSIXErrorCode.Type) -> Optional<POSIXErrorCode>'