support: Add helpers to create paths longer than PATH_MAX

Add new helpers support_create_and_chdir_toolong_temp_directory and
support_chdir_toolong_temp_directory to create and descend into
directory trees longer than PATH_MAX.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
(cherry picked from commit fb7bff12)