iOS14/Xcode12 libresolv is gone?

I've an existing app that is built using libresolv - it has calls to res_init(), res_query() and others. It uses these to lookup TXT records from a well-known, public location. When building under Xcode12 for an iOS14 target the following errors occur:

Code Block 
Undefined symbols for architecture x86_64:
  "_res_9_init", referenced from:
      _baseSeedQuery in BaselineCoreSafe.o
  "_res_9_query", referenced from:
      _baseSeedQuery in BaselineCoreSafe.o
  "_res_9_ns_initparse", referenced from:
      _baseSeedQuery in BaselineCoreSafe.o
  "_res_9_ns_parserr", referenced from:
      _baseSeedQuery in BaselineCoreSafe.o
  "_res_9_ns_sprintrr", referenced from:
      _baseSeedQuery in BaselineCoreSafe.o

The build is done with Swift PM and this portion of the code is built with:

Code Block 
      linkerSettings: [
                .linkedLibrary("resolv"),
                .linkedLibrary("pthread"),
                .linkedLibrary("bsd", .when(platforms: [.linux])),
            ]

For iOS14 is the res_* functionality in another library? Is there a different approach to use?

The Xcode 11 vs 12 contents aren't all that different:

Code Block $ find Xcode.app/ -name 'libres*.*' -print | grep iPhoneOS
Xcode.app//Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/lib/libresolv.9.tbd
Xcode.app//Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/lib/libresolv.tbd
$ find Xcode-beta.app/ -name 'libres*.*' -print | grep iPhoneOS
Xcode-beta.app//Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/lib/libresolv.dylib
Xcode-beta.app//Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/lib/libresolv.9.tbd
Xcode-beta.app//Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/lib/libresolv.9.dylib
Xcode-beta.app//Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/lib/libresolv.tbd

Is there a better build flag to use?