Install llvm-ar in the toolchain

[finagolfin]

A recent SPM change made it mandatory for there to be an archiver in the toolchain/PATH, swiftlang/swift-package-manager#5761, so make sure llvm-ar is bundled in the toolchain.

@compnerd and @tomerd, let me know what you think.

[compnerd]

I think that the build and packaging is good. Changing the default I'm less certain about. Arguably, we already have to do that with LTO, so this does simplify things, but honouring AR from the environment seems reasonable as that mirrors gcc and clang IIRC.

[finagolfin]

but honouring AR from the environment seems reasonable as that mirrors gcc and clang IIRC.

This simply changes the name of the default archiver looked for by the Swift compiler on Unix, it changes nothing about where it's looked for, ie you can still configure that by passing in a -tools-directory to the compiler or a wholly different archiver to SPM. The only real change is that we would be switching the default on Linux from ar in binutils to this llvm-ar we're now bundling in the Swift toolchain.

[finagolfin]

@MaxDesiatov, I see you're up, would you run the CI on this?

[MaxDesiatov]

I'd like to remind that as a frequent contributor you can get CI access, as described in the corresponding docs.

[MaxDesiatov]

@swift-ci please smoke test

[finagolfin]

@MaxDesiatov, as I mentioned to you the last time you reminded me, I'm winding down my port of Swift to Android and plan to submit only maybe 5-10 maintenance pulls in the coming year. With such a low frequency, I think it's better for security reasons that I don't have commit access, so I prefer to ask others to run the CI. If I'm bothering you in any way, please just say so and I will ask other committers from now on.

[finagolfin]

Building CMark on Linux and macOS failed because I changed the host archiver to llvm-ar too. I wasn't sure about that one as it depends on what is pre-installed on the CI host. Since it appears llvm-ar is not installed- Windows passed as it doesn't build CMark for some reason- should be fine to use the installed ar only to build the host compiler itself, removed that last change of the host archiver.

[finagolfin]

@egorzhdan, please run the CI again.

[egorzhdan]

@swift-ci please smoke test

[finagolfin]

Linux CI failed because I changed the default archiver name on Unix to llvm-ar and the static libdispatch build couldn't find it because the compiler uses what's installed in the host environment, as the freshly-built llvm-ar isn't installed in the same directory as the compiler yet. We could remedy this by installing llvm-ar on the linux CI, but I just changed back the default archiver used instead. We can always do that later, simply bundling an archiver in the toolchain should do for cross-compiling to Android for now.

@egorzhdan, one final CI run and this can go in.

[keith]

@swift-ci please smoke test

[finagolfin]

Alright, @compnerd, this is ready for review.

[finagolfin]

@keith, mind getting this in? I submitted this so we can get this mitigation in before the 5.8 branch tomorrow.

[compnerd]

Building and packaging the LLVM archiver is a good idea in general.

[compnerd]

Yeah, merging this before the 5.8 branch sounds reasonable. Thanks @buttaface!