Remove ignore-empty-index-file option

Summary:
Clang changes to remove this option and replace with a parameter
always set in the context of a ThinLTO distributed backend.

Depends on D33133.

Reviewers: pcc

Subscribers: mehdi_amini, eraman, cfe-commits

Differential Revision: https://reviews.llvm.org/D33134

llvm-svn: 302940
diff --git a/clang/lib/CodeGen/BackendUtil.cpp b/clang/lib/CodeGen/BackendUtil.cpp
index 51c21c9..0f07169 100644
--- a/clang/lib/CodeGen/BackendUtil.cpp
+++ b/clang/lib/CodeGen/BackendUtil.cpp
@@ -1073,7 +1073,8 @@
     // into memory and pass it into runThinLTOBackend, which will run the
     // function importer and invoke LTO passes.
     Expected<std::unique_ptr<ModuleSummaryIndex>> IndexOrErr =
-        llvm::getModuleSummaryIndexForFile(CGOpts.ThinLTOIndexFile);
+        llvm::getModuleSummaryIndexForFile(CGOpts.ThinLTOIndexFile,
+                                           /*IgnoreEmptyThinLTOIndexFile*/true);
     if (!IndexOrErr) {
       logAllUnhandledErrors(IndexOrErr.takeError(), errs(),
                             "Error loading index file '" +