Adhoc codesigning is corrupted by linker script

The Qt script we have been using to adopt objective-c namespaces is now causing problems since migrating our build servers to ARM: https://github.com/qt/qtbase/blob/dev/mkspecs/features/data/mac/objc_namespace.sh
 
As far as we could find out, the problem (= Apple complains about modified adhoc signature) is caused by the following pieces: * Since Xcode 12 the linker automatically signs the binaries ("linker signed", see https://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20201228/867028.html)

• The script modifies this existent signature (links twice as far as I could tell)
• Apple considers this "tampering" with the binary and raises a flag (spctl will tell: "invalid signature (code or signature have been modified)")
• This causes adhoc signed binaries to terminate the process with a SIGKILL (fatal for our unit tests)