Specify path to llvm build

Is there a way to tell the build-script the path to my llvm build directory? I usually have at least two builds of swift (sometimes three), and it would be great if I could point it to one llvm build folder instead of each having its own. I briefly looked at the docs and build scripts but couldn't find anything.

Thanks in advance!

You might want to be careful about that. Swift uses forked versions of llvm, clang, llbuild, etc., that have changes needed to support Swift that may or may not have been propagated upstream at any specific time. Those changes are potentially version specific, so that Apple's llvm-project repository may differ between, say, Swift 5.1, Swift 5.1.2, Swift 5.1.3, and Swift 5.2.

I'm talking about building the same source version of swift. For instance, right now, I'm building one for the linux buildbot preset, one for the macos buildbot preset, and one for my xcode build.

cc @Andrew_Trick I think you have your builds multiplexed this way, right?