Some tests fail because Xcode runs `POST_BUILD` commands before signing
the binaries they run. Tell the linker to perform ad-hoc codesign even
though Xcode normally tells it not to.
Other tests fail because `install_name_tool` does not revise ad-hoc
signatures without the codesign `linker-signed` flag. Add that flag
ourselves where needed by our tests.
For now these changes help our test suite pass so we can use it to cover
everything else. Both of these cases may need further investigation to
update CMake to help projects in general.
Issue: #21845, #21854
