[DoNotMerge][6.2][Caching] Reduce the number of cas ID passed on frontend commandline

[cachemeifyoucan]

• Explanation: Using IncludeTree::FileList to concat the include tree file systems that are passed on the command-line. This significantly reduce the command-line size, and also makes the cache key computation a lot faster.
• Scope: Make build log easier to read and also has performance benefits especially for batched builds.
• Issues: rdar://148752988
• Original PRs: [Caching] Reduce the number of cas ID passed on frontend commandline #81264
• Risk: Low. Swift caching only and no functional change intended.
• Testing: Unit Tests.
• Reviewers: @benlangmuir

[cachemeifyoucan]

Please testing with following PR:
swiftlang/llvm-project#10674

@swift-ci please test

[nkcsgexi]

This is a nice-to-have enhancement. Should we really cherry-pick to release/6.2?

[cachemeifyoucan]

This is a nice-to-have enhancement. Should we really cherry-pick to release/6.2?

There are lots of small performance improvements can be enabled after this. I don't expect all the changes will add up to significant amount but followup will not be possible without this. Maybe we can re-evaluate after I land all the changes on main and see the overall improvements and see if we should take all or not.

[nkcsgexi]

Thank you for the additional context, Steven! Yeah, it would be nice to consider what the overall benefits are before we deciding whether to cherry-pick them or not to the release/6.2 branch.