[bash-autocompletion] Fix bug when a flag ends with '='

There was a bug that when a flag ends with '=' and no value was suggested,
clang autocompletes the flag itself.
For example, in bash, it looked like this:
```
$ clang -fmodule-file=[tab]
-> $clang -fmodule-file=-fmodule-file
```
This is not what we expect. We expect a file autocompletion when no value
was found. With this patch, pressing tab suggests files in the current
directory.

Reviewers: teemperor, ruiu

Subscribers: cfe-commits
llvm-svn: 345121
diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
index f890a1d..583803d 100644
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -1534,7 +1534,9 @@
   if (SuggestedCompletions.empty())
     SuggestedCompletions = Opts->suggestValueCompletions(Cur, "");
 
-  if (SuggestedCompletions.empty()) {
+  // When flag ends with '=' and there was no value completion, return empty
+  // string and fall back to the file autocompletion.
+  if (SuggestedCompletions.empty() && !Cur.endswith("=")) {
     // If the flag is in the form of "--autocomplete=-foo",
     // we were requested to print out all option names that start with "-foo".
     // For example, "--autocomplete=-fsyn" is expanded to "-fsyntax-only".