[freeipa PR#3485][opened] configure.ac: don't rely on bashisms

[hermannch]

   URL: https://github.com/freeipa/freeipa/pull/3485
Author: hermannch
 Title: #3485: configure.ac: don't rely on bashisms
Action: opened

PR body:
"""
93fb037d8409d9d46606c31d8a240e3963b72651 introduced unportable shell
syntax, which led to erros like
./configure: 3179: ./configure: CFLAGS+= -D__STDC_WANT_LIB_EXT1__=1: not found
in case a posix shell is used.
"""

To pull the PR as Git branch:
git remote add ghfreeipa https://github.com/freeipa/freeipa
git fetch ghfreeipa pull/3485/head:pr3485
git checkout pr3485