swift

04f3751b - [Driver] Always fall back to an arclite in the Xcode default toolchain (#22923)

[Driver] Always fall back to an arclite in the Xcode default toolchain (#22923) ...instead of the current toolchain, which we would have just searched by looking relative to the swiftc binary. rdar://problem/48044350 (cherry picked from commit e76b5a847ced33291f96470ae40407f928dc31dd)