diff --git a/llvm/lib/ToolDrivers/llvm-lib/Options.td b/llvm/lib/ToolDrivers/llvm-lib/Options.td
--- a/llvm/lib/ToolDrivers/llvm-lib/Options.td
+++ b/llvm/lib/ToolDrivers/llvm-lib/Options.td
@@ -45,3 +45,4 @@
 
 def ltcg : F<"ltcg">;
 def nologo : F<"nologo">;
+def subsystem : P<"subsystem", "">;