In LLVM unified builds `%swift_obj_root` points to `<LLVM build dir>/tools/swift`,
and folders like `bin`, `lib` and `share` are not under `swift_obj_root`, which
makes some tests fail.
For the cases in which `%swift_obj_root/lib` was used, replace it by
using `%swift-lib-dir` instead. Replicate `%swift-lib-dir` to create
`%swift-bin-dir` and `%swift-share-dir`, and use those instead of
`%swift_obj_root/bin` and `%swift_obj_root/share`.
This alternates work both in Swift build-script builds and also in LLVM
unified builds.
- Virtual calls are done via a @llvm.type.checked.load instrinsic call with a type identifier
- Type identifier of a vfunc is the base method's mangling
- Type descriptors and class metadata get !type markers that list offsets and type identifiers of all vfuncs
- The -enable-llvm-vfe frontend flag enables VFE
- Two added tests verify the behavior on IR and by executing a program