Support: Fix handling of args that begin with @ but aren't files

Command line arguments that begin with @ but aren't a path to an
existing file currently cause later @file arguments to be ignored.

Correctly skip over these arguments instead of trying to read a
non-existent file 20 times and giving up.

Since the problem manifests in the clang driver, the test is in that
repository.

Fixes rdar://problem/15590906

llvm-svn: 196620
diff --git a/llvm/lib/Support/CommandLine.cpp b/llvm/lib/Support/CommandLine.cpp
index 9acaa08..7ed4dea 100644
--- a/llvm/lib/Support/CommandLine.cpp
+++ b/llvm/lib/Support/CommandLine.cpp
@@ -655,7 +655,10 @@
     // the cwd of the process or the response file?
     SmallVector<const char *, 0> ExpandedArgv;
     if (!ExpandResponseFile(Arg + 1, Saver, Tokenizer, ExpandedArgv)) {
+      // We couldn't read this file, so we leave it in the argument stream and
+      // move on.
       AllExpanded = false;
+      ++I;
       continue;
     }
     Argv.erase(Argv.begin() + I);