ENH: Ignore autocompletion clang helper files

The YouCompleteMe package for vim expansions
requires a file in the source tree to define
how the continous building of source files
for introspection needs to be done.

Change-Id: I221c3812e251752f43e37eafe65b160a73f18d30
Merge topic 'YouCompleteMePluginIgnore'

54c973e7 ENH: Ignore autocompletion clang helper files