Results in configure output like:
```
checking for X... no
/var/tmp/portage/sys-devel/gdb-12.1/work/gdb-12.1/gdb/configure: 18837: test: yes: unexpected operator
checking whether to use babeltrace... auto
```
... when /bin/sh is provided by a POSIX-compliant shell, like dash,
instead of bash.
fi
-if test "${enable_libbacktrace}" == "yes"; then
+if test "${enable_libbacktrace}" = "yes"; then
LIBBACKTRACE_INC="-I$srcdir/../libbacktrace/ -I../libbacktrace/"
LIBBACKTRACE_LIB=../libbacktrace/.libs/libbacktrace.a
esac],
enable_libbacktrace=yes)
-if test "${enable_libbacktrace}" == "yes"; then
+if test "${enable_libbacktrace}" = "yes"; then
LIBBACKTRACE_INC="-I$srcdir/../libbacktrace/ -I../libbacktrace/"
LIBBACKTRACE_LIB=../libbacktrace/.libs/libbacktrace.a
AC_DEFINE(HAVE_LIBBACKTRACE, 1, [Define if libbacktrace is being used.])