use autoconf macro to check for pkg-config (closes #15506)

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branch : 3.4
extra : source : 54939f3c1e176cdfd25cd12b779e36c7997ffb5a
Issue #23015: Improved testing of the uuid module.

--HG--
branch : 3.4
Issue #22777: Test pickling with all protocols.

--HG--
branch : 3.4
remove extra ssl imports (closes #23053)

Patch from Jan Matejek.

--HG--
branch : 3.4
extra : source : ebe8917189a33433084ac96ccb4e4680de34a137
asyncio doc: call_soon() does not call immediatly the callback. Patch written
by Martin Panter.

--HG--
branch : 3.4