vc-directory-exclusion-list

vc-directory-exclusion-list is a variable defined in `vc-hooks.el'.
Its value is

("SCCS" "RCS" "CVS" "MCVS" ".src" ".svn" ".git" ".hg" ".bzr" "_MTN" "_darcs" "{arch}")

Documentation:
List of directory names to be ignored when walking directory trees.

You can customize this variable.