Update podspec for v1.8.
Add CodeSignOnCopy, RemoveHeadersOnCopy attributes.
Silence warnings in XCTest framework.
Use proper variables in shell scripts.
Keep settings in xcconfig, remove unnecessary ones.
Properly set install names and rpaths for targets.
Copy Autoupdate.app in a separate phase.
Reduce duplication and macros.
Use Info.plist keys instead of macros.

This helps ensure that all code paths are compiled during development, reducing the chance of build errors (especially in CI). Additionally, developers can change these values without having to rebuild Sparkle (but it is still safe because modifying the plist will break the code-signing seal).
Further reduce macro usage.
Silence direct ivar access warning.