Set ad-hoc codesigning identity for macOS by default

CMakeLists.txt

@@ -2805,6 +2805,14 @@ if(APPLE AND MACOS_BUNDLE)
     set(BUNDLE_DIRS "${CMAKE_PREFIX_PATH}/lib;${Qt5Widgets_DIR}/../..")
     set(APPLE_CODESIGN_ENTITLEMENTS "${CMAKE_CURRENT_SOURCE_DIR}/packaging/macos/entitlements.plist")
 
+    # Starting with arm64 macOS Apple will require ad-hoc code signatures,
+    # which can be generated by setting the identity to a single dash (-).
+    # These only include a checksum for verifying integrity, not an actual
+    # signature.
+    if (NOT APPLE_CODESIGN_IDENTITY)
+      set(APPLE_CODESIGN_IDENTITY -)
+    endif()
+
     configure_file(cmake/modules/BundleInstall.cmake.in "${CMAKE_CURRENT_BINARY_DIR}/BundleInstall.cmake" @ONLY)
     install(SCRIPT "${CMAKE_CURRENT_BINARY_DIR}/BundleInstall.cmake")
 endif()