[ThinLTO] Clang side of renaming of function index (NFC)

This is the companion to an LLVM patch that renamed the function index
data structures and files to use the more general module summary index.

(Recommit after fixing LLVM side to add back missed file)

llvm-svn: 263514
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index eccf597..c212794 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -608,7 +608,7 @@
 
   Opts.PrepareForLTO = Args.hasArg(OPT_flto, OPT_flto_EQ);
   const Arg *A = Args.getLastArg(OPT_flto, OPT_flto_EQ);
-  Opts.EmitFunctionSummary = A && A->containsValue("thin");
+  Opts.EmitSummaryIndex = A && A->containsValue("thin");
   if (Arg *A = Args.getLastArg(OPT_fthinlto_index_EQ)) {
     if (IK != IK_LLVM_IR)
       Diags.Report(diag::err_drv_argument_only_allowed_with)