https://github.com/libcgroup/libcgroup/pull/243

From a363c163fdeb48e0536545ece856899ed97e99b2 Mon Sep 17 00:00:00 2001
From: Sam James <sam@gentoo.org>
Date: Sat, 10 Sep 2022 13:52:57 +0100
Subject: [PATCH] configure.ac: fix bashism

configure scripts need to be runnable with a POSIX-compliant /bin/sh.

On many (but not all!) systems, /bin/sh is provided by Bash, so errors
like this aren't spotted. Notably Debian defaults to /bin/sh provided
by dash which doesn't tolerate such bashisms as '=='.

This retains compatibility with bash.

Fixes configure warnings/errors like:
```
checking whether to build static libraries... no
./configure: 14089: test: xno: unexpected operator
checking for x86_64-pc-linux-gnu-g++... x86_64-pc-linux-gnu-g++
```

Signed-off-by: Sam James <sam@gentoo.org>
--- a/configure.ac
+++ b/configure.ac
@@ -137,7 +137,7 @@ AC_ARG_ENABLE([opaque-hierarchy],
 AC_ARG_ENABLE([tests],
       [AS_HELP_STRING([--enable-tests],[compile libcgroup tests [default=yes]])],
       [
-		if test "x$enableval" == xno; then
+		if test "x$enableval" = xno; then
 			with_tests=false
 		else
 			with_tests=true