Raw values of enum cases from another module are not specified in the declaration of the enum unless that enum is `@objc`. This meant that `EnumRawValuesRequest` was computing potentially incorrect raw values when the enum declaration supported it and was emitting incorrect diagnostics for other enum decls.
Resolves SR-14355 and rdar://75451691
The `-force-single-frontend-invocation` flag predates WMO and is now an
alias for `-whole-module-optimization`. We should use the latter and let
the former fade into history.
