configure: fix check_min_lib_version() eval

configure: fix check_min_lib_version() eval

The following shell statement:

  if eval "echo \$$_feature" = "yes" ; then

executes:

  echo $... = "yes"

It does not actually compare the variable named by $_feature to the
string "yes".

Add the missing "test" call so the comparison happens as intended and
wrap the eval so it doesn't include the = "yes".

Fixes: 3e48f7c9de61 ("configure: fix syntax error with NetBSD")
Cc: Dmitry Fomichev <dmitry.fomichev@wdc.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>