Revert "Revert "Make the DWARF version emitted by the Swift compiler configurable.""

include/swift/Driver/Driver.h

@@ -125,6 +125,9 @@ public:
   /// What kind of debug info to generate.
   IRGenDebugInfoFormat DebugInfoFormat = IRGenDebugInfoFormat::None;
 
+  /// DWARF output format version number.
+  std::optional<uint8_t> DWARFVersion;
+
   /// Whether or not the driver should generate a module.
   bool ShouldGenerateModule = false;