IMPORT: slz: silence a build warning with -Wundef

The test on FIND_OPTIMAL_MATCH for the experimental code can yield a
build warning when using -Wundef, let's turn it into a regular ifdef.

This is slz upstream commit 05630ae8f22b71022803809eb1e7deb707bb30fb

(cherry picked from commit fc89c3fd2b773e67c351f74459401ab6b8ac6c8c)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
1 file changed