Add https://www.gnu.org/software/autoconf-archive/ax_check_openssl.html
to auto-detect compiler flags, linker flags and libraries to compile
OpenSSL extensions. The M4 macro uses pkg-config and falls back to
manual detection.

Add autoconf magic to detect usable X509_VERIFY_PARAM_set1_host()
and related functions.

Refactor setup.py to use new config vars to compile _ssl and _hashlib
modules.
Signed-off-by: Christian Heimes <christian@python.org>