Simplify the SDK layout

[compnerd]

Description

We currently have a SDK layout of:

/usr/lib/swift/<platform>/<arch>

It would be nice to simplify this down to /usr/lib or /usr/lib/<triple> to allow a simpler SDK construction.

Additional information

No response

[compnerd]

CC: @etcwilde

[etcwilde]

Yes please. If we do reduce it like this, CMake will handle setting up the install paths correctly without us needing to do anything clever.

[finagolfin]

Are you suggesting getting rid of /usr/lib/swift/<platform>/<arch>/ alone or /usr/lib/swift/ altogether? If the former, there are very few files left in there for most platforms, a few remaining swiftmodules, the libc header/modulemap, and the small runtime object file:

> ls swift-DEVELOPMENT-SNAPSHOT-2025-01-05-a-fedora39/usr/lib/swift/linux/x86_64/
Dispatch.swiftdoc     glibc.modulemap  swiftrt.o        XCTest.swiftmodule
Dispatch.swiftmodule  SwiftGlibc.h     XCTest.swiftdoc

If the latter, the problem is that it is a mix of various headers and libraries, some of which collide with system packages like libdispatch:

> ls swift-DEVELOPMENT-SNAPSHOT-2025-01-05-a-fedora39/usr/lib/swift/
apinotes  CoreFoundation  _FoundationCShims     host                        linux     pm
Block     dispatch        _foundation_unicode   _InternalSwiftScan          migrator  shims
clang     embedded        FrameworkABIBaseline  _InternalSwiftStaticMirror  os        swiftToCxx

I've moved the Swift runtime libraries in the Termux app for Android into <sysroot>/usr/lib/, well, technically symlinks to them. But just like our Swift-forked lldb and clang collide with system packages, I don't see anybody putting in the effort to move all the rest of this.