* configure.ac: Fix configure.ac bashisms

Reported-by: Brian Inglis
18 jobs for tmp-fix-configure-bashisms in 15 minutes and 49 seconds (queued for 1 second)
Status Job ID Name Coverage
  Stage1 Testing
passed #822717387
shared linux
Alpine

00:04:28

passed #822717389
shared linux
Arch

00:04:26

passed #822717390
CommitCheck

00:00:22

passed #822717391
shared linux
Debian/HTTP2

00:08:36

passed #822717376
shared linux
Debian/OpenSSL

00:07:38

passed #822717370
shared linux
Debian/Testing

00:05:16

passed #822717372
shared linux
Debian/Unstable

00:07:40

passed #822717374
shared linux
Debian/WolfSSL

00:07:28

passed #822717393
freebsd
FreeBSD.x86_64

00:02:04

passed #822717369
shared linux
Full+VPATH/Debian

00:07:08

canceled #822717388
shared linux allowed to fail
MinGW64

00:15:43

passed #822717377
shared
Minimal/Debian

00:04:50

passed #822717378
shared linux
Sanitizers/Debian

00:05:11

passed #822717380
shared linux
Scan-Build/Debian

00:09:22

passed #822717385
shared linux
Simple/Fedora

00:05:27

canceled #822717382
shared linux
Valgrind/Debian

00:15:44

canceled #822717383
shared linux
Valgrind/i386

00:15:44

 
  Stage2 Tarball
canceled #822717396
shared linux
Tarball