Add the returns_twice attribute to LLVM.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@141001 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/AsmParser/LLLexer.cpp b/lib/AsmParser/LLLexer.cpp
index fdadd1b..029f942 100644
--- a/lib/AsmParser/LLLexer.cpp
+++ b/lib/AsmParser/LLLexer.cpp
@@ -558,6 +558,7 @@
   KEYWORD(readnone);
   KEYWORD(readonly);
   KEYWORD(uwtable);
+  KEYWORD(returns_twice);
 
   KEYWORD(inlinehint);
   KEYWORD(noinline);