The current .clang-format file is not valid for clang-format versions 3.5 and below. The attached patch would 'fix' this by removing key words not known in version 3.5, but still wouldn't work for versions below that. I do not suggest to apply the patch - it should just show that this is quite some number.
Looking at the .clang-format file it seems that it does not use one of the pre-defined styles, but rather creates it's own (even if it is based on one given the comment in the file). I wonder if all of this is really necessary, or if we could not simply use one of the pre-defined styles, possibly with a few changes that work across clang-format versions.