install(EXPORT): Check for missing file sets at generate time
Missing file sets were originally checked at configure time in install(TARGETS ... EXPORT), but were not checked at generate time. If a file set was added after install(TARGETS ... EXPORT) was called, an abortion error was thrown. Check again at generate time to gracefully display an error message instead of crashing.
Fixes: #23680 (closed)
Backport: release
Edited by Kyle Edwards