./configure: add ability to build and install only shared library (without static libpython3.a)

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2017-08-12.18:04:09.034>
labels = ['build']
title = './configure: add ability to build and install only shared library (without static libpython3.a)'
updated_at = <Date 2017-08-12.18:04:09.034>
user = 'https://bugs.python.org/dilyanpalauzov'

bugs.python.org fields:

activity = <Date 2017-08-12.18:04:09.034>
actor = 'dilyan.palauzov'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Build']
creation = <Date 2017-08-12.18:04:09.034>
creator = 'dilyan.palauzov'
dependencies = []
files = []
hgrepos = []
issue_num = 31190
keywords = []
message_count = 1.0
messages = ['300206']
nosy_count = 1.0
nosy_names = ['dilyan.palauzov']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue31190'
versions = []