python-six: Error fix for recipes depend on python-six

If you bitbake recipes which depends on python-six such as
python-cryptography. And also your network is not very well.
Error will occur as following:
   Download error on https://pypi.python.org/simple/six/

:
   [Errno -5] No address associated with hostname -- Some packages may not be found!
    Couldn't find index page for 'six' (maybe misspelled?)
    No local packages or download links found for six
So add do_compile_append() to fix it.

Signed-off-by: Li Xin <lixin.fnst@cn.fujitsu.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>