[libevent] add features

[NancyLi1013]

Add openssl and thread features for libevent.
libevhtp needs to depend on this two features.
Related issue #4793.

[NancyLi1013]

/azp run

[vicroms]

/azp run

[NancyLi1013]

The failure on Linux is due to:

/ci/myagent/_work/1/s/installed/x64-linux/debug/lib/libevent.a /ci/myagent/_work/1/s/installed/x64-linux/debug/lib/libevent_core.a /ci/myagent/_work/1/s/installed/x64-linux/debug/lib/libevent_extra.a -levent_openssl_static /ci/myagent/_work/1/s/installed/x64-linux/debug/lib/libglog.a -lpthread /ci/myagent/_work/1/s/installed/x64-linux/debug/lib/libgflags_debug.a -lpthread && :
/usr/bin/ld: cannot find -levent_openssl_static
collect2: error: ld returned 1 exit status

It seems that there is no event_openssl installed here.
I try to checkout this branch to my local and do as the following steps:

1. vcpkg install libevent[openssl] .
2. vcpkg install evpp

Then the failure disappeared.
So I guess we need to install openssl feature manually to test this issue.

[NancyLi1013]

All features test pass with below triplets:

• x86-windows

• x64-windows-static

• arm64-windows

• x64-linux

Note: This port currently doesn't support UWP.

[ras0219-msft]

LGTM!

[sipsorcery]

The thread EVENT__DISABLE_THREAD_SUPPORT change in this PR has broken the Bitcoin Core msvc build.

I can work around it by using a custom port but was wondering if that change was required for a particular feature? It's not clear from the PR description.

[vicroms]

Hi @sipsorcery

We usually disable optional library features by default and make them accessible through package features.

In this case, you might not need a custom port and can just simply re-enable EVENT__DISABLE_THREAD_SUPPORT by doing:

./vcpkg install libevent[threads]

[vicroms]

@NancyLi1013
@ras0219-msft

Shouldn't threads be a default feature of this port?

[sipsorcery]

@vicroms thx for the response. Somehow I missed "Feature Packages" being added to vcpkg. Once it got pointed out to me we were able to update the vcpkg list to use libevent[threads] and our build is working again.

+1 for threads being the default.

[NancyLi1013]

Hi @sipsorcery thanks for reporting this issue.
@vicroms thanks for your detail explanation to this issue.

I will add thread as the default feature of this port.