[CMake] Simplify two binary variables into one tri-state variable

[davezarzycki]

Also remove some ancient logic to detect and ignore requests to use LLD. If people want to explicitly use LLD, they probably have a reason and we shouldn't second guess them.

[davezarzycki]

@swift-ci please test

[compnerd]

Making the Swift build system more similar to the LLVM options is definitely a good idea.

[compnerd]

I think that we should simplify this like the previous case in cmake/modules/AddSwift.cmake

[drodriguez]

The parts that I know (the Android parts, mostly), looks fine to me. Should be functionally equivalent to the existing code. There's only that one point that should be double checked. Otherwise looks good.

[drodriguez]

I think the manipulations around these lines (L418-L422) are the same to the ones in AddSwiftUnittests.cmake, but the modifications are different: some checks are kept here, while they are drop in the other file. Is the divergence intentional?

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - fce4f52df219a516c761b4dbe108370352ad46ba

[davezarzycki]

Hi @compnerd and @drodriguez – I've simplified AddSwiftStdlib.cmake more. I think we should make SWIFT_USE_LINKER be as much like LLVM_USE_LINKER as possible. In other words, if it's set, trust it.

@swift-ci please test

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - fce4f52df219a516c761b4dbe108370352ad46ba

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - fce4f52df219a516c761b4dbe108370352ad46ba

[davezarzycki]

@swift-ci please clean test linux

[compnerd]

Yeah, I agree on the idea that if the user specified it, we assume correct and honor it.

[davezarzycki]

@swift-ci please test windows