LibRegex: Allow the SingleMatch flag to be used as a PosixFlag

Author: https://github.com/water-ghosts
Commit: 5bf2cce839
Pull-request: https://github.com/SerenityOS/serenity/pull/16584
Reviewed-by: https://github.com/ADKaster ✅
Reviewed-by: https://github.com/gmta
Reviewed-by: https://github.com/kleinesfilmroellchen
Reviewed-by: https://github.com/rtobar

Userland/Libraries/LibRegex/RegexOptions.h

@@ -53,6 +53,7 @@ enum class PosixFlags : FlagsUnderlyingType {
     SkipSubExprResults = (FlagsUnderlyingType)AllFlags::SkipSubExprResults,
     SkipTrimEmptyMatches = (FlagsUnderlyingType)AllFlags::SkipTrimEmptyMatches,
     Multiline = (FlagsUnderlyingType)AllFlags::Multiline,
+    SingleMatch = (FlagsUnderlyingType)AllFlags::SingleMatch,
     StringCopyMatches = (FlagsUnderlyingType)AllFlags::StringCopyMatches,
 };