[build-script-impl] Allow cross-compiling the host toolchain for Android

[finagolfin]

This was needed in order to cross-compile the Swift compiler for Android AArch64, which is why it is now available on any Android AArch64 device running 7.0 Nougat or later. Simply install the Termux app and run pkg install swift and you have a working Swift 5.2.1 compiler. I ran the Swift validation suite with this cross-compiled compiler and 90% of the tests passed, with the remaining failing mostly because they were missing host test binaries like sourcekitd-test.

@drexin, one last tiny Android patch extracted from my Termux packaging scripts that should be safe to merge.

[drexin]

@swift-ci smoke test

[finagolfin]

Passes all CI, ready to go.

[finagolfin]

@drexin or @drodriguez, can we get this one-liner in before the 5.3 branch?

[drodriguez]

Can this be android-* like the ones at the start of the line? Thanks.

[finagolfin]

I've never tried anything other than AArch64, but I guess the others would work too. I'll change it.

[drodriguez]

@swift-ci please test

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - fb5273822590e53de264a44350409d198eacbbe7

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - fb5273822590e53de264a44350409d198eacbbe7

[drexin]

LGTM, thanks

[finagolfin]

Thanks.

@drexin, would you like me to submit a backport of #30565 for the 5.2 branch? If you try to build the whole Swift 5.2 toolchain with ./swift/utils/build-script --install-prefix=/opt --xctest -b -p, it fails when building SwiftPM on non-Darwin platforms, but that worked with 5.1 and I'm guessing even before, which is why I had to apply parts of that patch to my Android package of Swift 5.2. Or, this regression could just be ignored for now, since the fix is in the 5.3 branch. Just let me know what you want.

[drexin]

@buttaface This is not on 5.3, yet. If you want it on 5.3, you have to backport it to release/5.3.

[drexin]

Up to you if you also want it on 5.2.

[finagolfin]

@drexin, there's a misunderstanding: I'm not talking about this pull but a different one, #30565, which has to do with the install prefix used by the build-script on non-Darwin platforms. That one was merged before the 5.3 branch, but I'm not sure if you want it in 5.2.

[drexin]

Ah, yes. It‘s really up to you if you want it in 5.2 or not. It‘s not up to me what gets merged anyway 🙂