libh2o-evloop is not linked with wslay

[Pieter Lexis]

When attempting to link against the libh2o-evloop provided with Ubuntu Bionic (2.2.4+dfsg-1build1) and Ubuntu Cosmic (2.2.5+dfsg1-6), the linking step fails with the following errors:

```
/usr/bin/ld: /usr/lib/x86_64-linux-gnu/libh2o-evloop.so: undefined reference to `wslay_event_want_read'
/usr/bin/ld: /usr/lib/x86_64-linux-gnu/libh2o-evloop.so: undefined reference to `wslay_event_set_error'
/usr/bin/ld: /usr/lib/x86_64-linux-gnu/libh2o-evloop.so: undefined reference to `wslay_event_recv'
/usr/bin/ld: /usr/lib/x86_64-linux-gnu/libh2o-evloop.so: undefined reference to `wslay_event_context_free'
/usr/bin/ld: /usr/lib/x86_64-linux-gnu/libh2o-evloop.so: undefined reference to `wslay_event_want_write'
/usr/bin/ld: /usr/lib/x86_64-linux-gnu/libh2o-evloop.so: undefined reference to `wslay_event_send'
/usr/bin/ld: /usr/lib/x86_64-linux-gnu/libh2o-evloop.so: undefined reference to `wslay_event_context_server_init'
```

According to this (https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=908124) debian bug, it seems libh2o-evloop.so is not linked with libwslay. Please pull in the patch from Debian(https://sources.debian.org/patches/h2o/2.2.5+dfsg2-2/link-against-wslay.patch/) to make libh2o-evloop usable again.

[Dylan Aïssi (daissi)]

Fixed in Disco with h2o 2.2.5+dfsg2-1

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.