Merge pull request #42140 from artemcm/EnableRegexLiteralFlag

Add support for `-enable-regex-literals` flag

include/swift/Basic/LangOptions.h

@@ -561,6 +561,9 @@ namespace swift {
     /// Enables dumping type witness systems from associated type inference.
     bool DumpTypeWitnessSystems = false;
 
+    /// Enables `/.../` syntax regular-expression literals
+    bool EnableForwardSlashRegexLiterals = false;
+
     /// Sets the target we are building for and updates platform conditions
     /// to match.
     ///