Merge branch 'jw/builtin-objectmode-attr'

The builtin_objectmode attribute is populated for each path
without adding anything in .gitattributes files, which would be
useful in magic pathspec, e.g., ":(attr:builtin_objectmode=100755)"
to limit to executables.

* jw/builtin-objectmode-attr:
  attr: add builtin objectmode values support

diff --cc t/t6135-pathspec-with-attrs.sh
Simple merge