Add a test for r263577: "Add missing error handling in llvm-lto"

On Rafael's suggestion!
(also fix a discrepancy between this error message format and the others)

From: Mehdi Amini <mehdi.amini@apple.com>
llvm-svn: 263860

llvm/test/tools/llvm-lto/error.ll

@@ -3,3 +3,6 @@
 
 ; RUN: not llvm-lto --list-symbols-only %S/Inputs/empty.bc 2>&1 | FileCheck %s --check-prefix=CHECK-LIST
 ; CHECK-LIST: llvm-lto: error loading file '{{.*}}/Inputs/empty.bc': The file was not recognized as a valid object file
+
+; RUN: not llvm-lto --thinlto %S/Inputs/empty.bc 2>&1 | FileCheck %s --check-prefix=CHECK-THIN
+; CHECK-THIN: llvm-lto: error loading file '{{.*}}/Inputs/empty.bc': The file was not recognized as a valid object file

llvm/tools/llvm-lto/llvm-lto.cpp

@@ -258,7 +258,7 @@ static void createCombinedModuleSummaryIndex() {
     CurrentActivity = "loading file '" + Filename + "'";
     ErrorOr<std::unique_ptr<ModuleSummaryIndex>> IndexOrErr =
         llvm::getModuleSummaryIndexForFile(Filename, diagnosticHandler);
-    error(IndexOrErr, "error: " + CurrentActivity);
+    error(IndexOrErr, "error " + CurrentActivity);
     std::unique_ptr<ModuleSummaryIndex> Index = std::move(IndexOrErr.get());
     CurrentActivity = "";
     // Skip files without a module summary.