[llvm-readobj] reportError() never returns. Mark with the correct attribute.

llvm-svn: 254752
diff --git a/llvm/tools/llvm-readobj/llvm-readobj.cpp b/llvm/tools/llvm-readobj/llvm-readobj.cpp
index 63cec03..5406aff 100644
--- a/llvm/tools/llvm-readobj/llvm-readobj.cpp
+++ b/llvm/tools/llvm-readobj/llvm-readobj.cpp
@@ -231,7 +231,7 @@
 
 namespace llvm {
 
-void reportError(Twine Msg) {
+LLVM_ATTRIBUTE_NORETURN void reportError(Twine Msg) {
   outs() << "\nError reading file: " << Msg << ".\n";
   outs().flush();
   exit(1);