[Coroutines] Add header guard to header that's missing one.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@293494 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Coroutines/CoroInstr.h

@@ -23,6 +23,9 @@
 // the Coroutine library.
 //===----------------------------------------------------------------------===//
 
+#ifndef LLVM_LIB_TRANSFORMS_COROUTINES_COROINSTR_H
+#define LLVM_LIB_TRANSFORMS_COROUTINES_COROINSTR_H
+
 #include "llvm/IR/GlobalVariable.h"
 #include "llvm/IR/IntrinsicInst.h"
 
@@ -316,3 +319,5 @@ public:
 };
 
 } // End namespace llvm.
+
+#endif