Bug#839224: python-systemd: "undefined symbol" error on armhf

[Zbigniew Jędrzejewski-Szmek]

Oops, I forgot I fixed this in git after tagging v232 (commit 8024fc6171).
I now added -Werror=implicit-function-declaration to compile flags so the
compilation should actually fail instead of just emitted a warning if the
same problem occurs hain.

You probably want to pull in most of those:

* 84fcfc05e5 setup.py: make build fail if undeclared symbols are used
* 911591a118 build-sys: import "pytest" instead of "py.test"
* 8024fc6171 _reader: use proper ifdef guard for sd_j_open_files_fd
* 35a5b281ad tests: add workaround for pre-232 system returning EINVAL on some flags
* b9767792b9 docs: fix sphinx format warning
* 177ac6d894 tests: skip fdstore tests if not implemented

Zbyszek