Add vs_files.ciopfs to gitignore

Change-Id: I66bfe94e5625715e03ee00b534a27003ca688047
Reviewed-on: https://chromium-review.googlesource.com/747073
Commit-Queue: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>

.gitignore

@@ -44,6 +44,7 @@
 /win_toolchain/*.timestamps
 /win_toolchain/.vspro
 /win_toolchain/data.json
+/win_toolchain/vs_files.ciopfs
 
 # Ignore ctags/cscope index files
 /TAGS