Redirect stderr when calling `swift -version` (#718)
Redirect stderr when calling `swift -version` (#718)

Since this is using `popen`, we were capturing stdout, but stderr could still end up on the terminal. In particular, the Swift driver version could be intermingled with other output in tools using llbuild such as SwiftPM, because it is being printed to stderr: https://github.com/apple/swift-driver/blob/main/Sources/SwiftDriver/Driver/Driver.swift#L989
apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild