devel/pecl-msgpack: reinstate IGNORE_WITH_PHP=86
Dependency devel/pecl-APCu is not yet available for php86.
Please make sure you test the port in the php86 flavour before
reenabling the option.
Fixes: 4390d463875b81a5948541e3b27275d30aad54e2
Approved by: portmgr (build fix blanket)