Return true on success in cl::ExpandResponseFiles

This fixes a logic bug pointed out by Juraj Ivancic.

No behavior change because none of the in-tree clients of
cl::ExpandResponseFiles check the return value.  In this case, the
@prefixed arguments are left in the command line.  Downstream command
line processing has the opportunity to emit errors about it, so this
isn't that bad.

llvm-svn: 196306
diff --git a/llvm/lib/Support/CommandLine.cpp b/llvm/lib/Support/CommandLine.cpp
index 44a88d8..9acaa08 100644
--- a/llvm/lib/Support/CommandLine.cpp
+++ b/llvm/lib/Support/CommandLine.cpp
@@ -634,7 +634,7 @@
 bool cl::ExpandResponseFiles(StringSaver &Saver, TokenizerCallback Tokenizer,
                              SmallVectorImpl<const char *> &Argv) {
   unsigned RspFiles = 0;
-  bool AllExpanded = false;
+  bool AllExpanded = true;
 
   // Don't cache Argv.size() because it can change.
   for (unsigned I = 0; I != Argv.size(); ) {