Hi, I've already reported this bug as https://bugs.swift.org/browse/SR-14788, but I also wanted to post here in the hopes that somebody's stumbled upon the same thing (and had found a workaround).
In a nutshell: I have a Swift package with Objective-C code that depends on another package with Swift code. When building it without code coverage enabled, everything builds fine. When code coverage is turned on, I get undefined symbols. Ideally I'd rewrite this code to Swift, but that's not feasible at the moment.
StackOverflow mentions adding
-fprofile-instr-generate to linker flags, but I don't know if that is even possible in a package manifest (or at least without using unsafe flags).