Define HAVE_MKDIR when building for NaCl

This should enable mktemp() to work. Without this newlib's
mkdtemp always return ENOSYS.

BUG= https://code.google.com/p/nativeclient/issues/detail?id=4017
R=mcgrathr@chromium.org

Review URL: https://codereview.chromium.org/795283003
1 file changed