This has been going on at least since Xcode 8 when apple replaced links to dylib with the text tbd files.
On travis, build image: xcode 9.2, osx 10.12, compiler: clang; when building any code that uses a framework and you are not using Xcode but from the command line witih makefile or ninja or whatever, there are always these
ld: warning: text-based stub file /System/Library/Frameworks//AudioToolbox.framework/AudioToolbox.tbd
and library file /System/Library/Frameworks//AudioToolbox.framework/AudioToolbox are out of sync.
Falling back to library file for linking.
This is Xcode's linker, ld.
There are no other external compilers installed, this is a fresh travis build with no ccache. This is only a sample build which uses this framework but if i called other frameworks Accelerate, ************, OpenCL, OpenGL, they will all throw these warnings.
If you attempt to build with macports clang 4,5,6, the build build will bomb even with the latest ld installed.