runtime: explicitly namespace ArrayRef in shared headers

[compnerd]

There are a set of headers shared between the Swift compiler and the
runtime. Ensure that we explicitly use llvm::ArrayRef rather than
ArrayRef which is aliased to ::llvm::ArrayRef. Doing so enables us
to replace the ArrayRef with an inline namespaced version fixing ODR
violations when the swift runtime is loaded into an address space with
LLVM.

Replace this paragraph with a description of your changes and rationale. Provide links to external references/discussions if appropriate.

Resolves SR-NNNN.

[compnerd]

CC: @mikeash @DougGregor @jckarter @rjmccall

[compnerd]

@swift-ci please test

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - 4482b4ebe97508947286c6424d1c1df2e9566437

[compnerd]

@swift-ci please test

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 4482b4ebe97508947286c6424d1c1df2e9566437

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - 4482b4ebe97508947286c6424d1c1df2e9566437

[compnerd]

@swift-ci please test

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - 4482b4ebe97508947286c6424d1c1df2e9566437

[shahmishal]

@swift-ci please test windows

[rjmccall]

Looks like you have whitespace problems everywhere you've spelled out llvm::ArrrayRef.

I don't know how spelling out llvm::ArrayRef in a bunch of places is easier to make use an inline namespace than a using declaration in a common location. I also don't know what ODR problems you could possibly be having with ArrayRef.

[compnerd]

I can re-clang-format the changed areas. The explicit spelling helps by allowing the swift runtime to have a completely isolated __swift::__runtime::llvm::ArrayRef while allowing the compiler to use llvm::ArrayRef. The forward declaration causes the conflict and the inline namespace is ignored. I've simply removed the forward declaration in the runtime path, and adjusted the invocations accordingly.

The ODR violations that I am referring to occur when LLVM libraries are used in the same address space as the Swift runtime and are at different versions. There are collisions which occur due to the runtime's use of the llvm::. By isolating the LLVMSupport usage into an inline namespace, we can avoid the collision.

[compnerd]

@rjmccall thanks for pointing out the whitespace issue, I really missed that. Ran clang-format over the patch again, definitely something went wrong originally.

[compnerd]

@swift-ci please test

[compnerd]

@swift-ci please test Windows platform