libffi detection via pkg-config is broken

[yan12125]

BPO	33619
Nosy	@warsaw, @benjaminp, @yan12125
PRs	bpo-33619: Fix libffi detection by regenerating ./configure #7075

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2018-05-24.06:37:17.713>
created_at = <Date 2018-05-23.16:34:24.904>
labels = ['build', '3.8']
title = 'libffi detection via pkg-config is broken'
updated_at = <Date 2018-05-24.06:37:17.712>
user = 'https://github.com/yan12125'

bugs.python.org fields:

activity = <Date 2018-05-24.06:37:17.712>
actor = 'benjamin.peterson'
assignee = 'none'
closed = True
closed_date = <Date 2018-05-24.06:37:17.713>
closer = 'benjamin.peterson'
components = ['Build']
creation = <Date 2018-05-23.16:34:24.904>
creator = 'yan12125'
dependencies = []
files = []
hgrepos = []
issue_num = 33619
keywords = ['patch']
message_count = 2.0
messages = ['317424', '317537']
nosy_count = 3.0
nosy_names = ['barry', 'benjamin.peterson', 'yan12125']
pr_nums = ['7075']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'compile error'
url = 'https://bugs.python.org/issue33619'
versions = ['Python 3.8']

[yan12125]

The cause is that ./configure contains unexpanded m4 macro PKG_PROG_PKG_CONFIG:

https://github.com/python/cpython/blob/3055c94/configure#L9909

For unknown reasons, after #51099 the PKG_PROG_PKG_CONFIG macro is removed from aclocal.m4, and thus the macro is kept unexpanded in ./configure. As a result, $PKG_CONFIG is not correctly set, libffi can't be detected and thus _ctypes fails to build.

Run autoreconf again fixes the issue on my machine. I have pkg-config 0.29.2-1, autoconf 2.69-4 and automake 1.15.1-1 on Arch Linux.

cc the author of #51099

[benjaminp]

New changeset 03c0d2e by Benjamin Peterson (Chih-Hsuan Yen) in branch 'master':
closes bpo-33619: Fix libffi detection by regenerating ./configure (GH-7075)
03c0d2e