dyld error with swda in macOS 10.13.6

[SMcCandlish]

$ swda -?

dyld: Symbol not found: _$s15_ObjectiveCTypes01_A11CBridgeablePTl
  Referenced from: /Users/smccandlish/Downloads/temp/SwiftDefaultApps-v2.0.1/swda
  Expected in: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/macosx/libswiftCore.dylib
 in /Users/smccandlish/Downloads/temp/SwiftDefaultApps-v2.0.1/swda
Abort trap: 6

Maybe this is some super-duper-obvious thing to Swift devs, but not so much for me. I'm mostly a Linux/Unix guy. The library in question is present:

$ ls -al /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/macosx/libswiftCore.dylib

-rwxr-xr-x 3 smccandlish wheel 6544080 Oct 19  2018 /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/macosx/libswiftCore.dylib*