Fixing a warning about control reaching the end of a non-void function.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188524 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/utils/TableGen/CodeGenInstruction.cpp b/utils/TableGen/CodeGenInstruction.cpp
index 3673204..8ec7682 100644
--- a/utils/TableGen/CodeGenInstruction.cpp
+++ b/utils/TableGen/CodeGenInstruction.cpp
@@ -192,6 +192,7 @@
 
   // Otherwise, didn't find it!
   PrintFatalError(TheDef->getName() + ": unknown suboperand name in '" + Op + "'");
+  return std::make_pair(0U, 0U);
 }
 
 static void ParseConstraint(const std::string &CStr, CGIOperandList &Ops) {