[Options] Add missing -sil-output-dir and ir-output-dir flag

The swift-driver flags need to be declared in Options.td. Add the
missing driver flags in swift-driver#1995

Author: cachemeifyoucan

include/swift/Option/Options.td

@@ -377,6 +377,16 @@ def pch_output_dir: Separate<["-"], "pch-output-dir">,
   Flags<[FrontendOption, HelpHidden, ArgumentIsPath]>,
   HelpText<"Directory to persist automatically created precompiled bridging headers">;
 
+def sil_output_dir: Separate<["-"], "sil-output-dir">,
+  Flags<[ArgumentIsPath, SupplementaryOutput]>,
+  HelpText<"Output SIL files to directory <dir> as additional output during compilation">,
+  MetaVarName<"<dir>">;
+
+def ir_output_dir: Separate<["-"], "ir-output-dir">,
+  Flags<[ArgumentIsPath, SupplementaryOutput]>,
+  HelpText<"Output LLVM IR files to directory <dir> as additional output during compilation">,
+  MetaVarName<"<dir>">;
+
 def auto_bridging_header_chaining: Flag<["-"], "auto-bridging-header-chaining">,
   Flags<[FrontendOption, HelpHidden]>,
   HelpText<"Automatically chaining all the bridging headers">;