Undefined symbol: ___isOSVersionAtLeast

Using Swift
21

I have downloaded the Swift 5.1.2 Release 2019-11-30 (a) Toolchain with Xcode Version 11.1 (11A1027)
But i am getting [Undefined symbol: ___isOSVersionAtLeast]
How to copy files

22

I was able to follow the instructions by @Mike_Ash just fine - naturally with updated directory paths to match the version of the tool chain that you are using.
Depending on what you are trying to do, you could perhaps also just use the tool chain included in Xcode 11.4, which does not have the issue.

23

This is still a problem.

Had to mod Mike Ash's command like this:

sudo cp /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/11.0.3/lib/darwin/libclang_rt.*.a /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2020-06-08-a.xctoolchain/usr/lib/clang/10.0.0/lib/darwin/
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24

Perfect
Thank you for your support

25

photo_2020-09-17 01.54.08
It is happening with the brand new Swift 5.3 released on Swift.org (version of September 16, 2020)
If I use embedded Xcode 12 toolchain everything compiles fine, if I select Swift 5.3 downloaded from the swift.org it fails with these errors.

26

I filed Undefined symbol: ___isOSVersionAtLeast with macOS toolchains · Issue #62626 · apple/swift · GitHub about this with the workarounds from here

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