Fix bashisms in configure.ac
Fix bashisms in configure.ac

'==' is not supported in POSIX shells. = is equivalent for us, so let's
use that instead.

This led to breakage when using e.g. dash as the system shell (rather than Bash)
as it caused support for e.g. gssproxy to be misdetected and broken binaries
were produced.

Bug: https://bugs.gentoo.org/762823
Signed-off-by: Sam James <f16bed56189e249fe4ca8ed10a1ecae60e8ceac0@gentoo.org>

latchset/libverto,latchset/libverto