HHVM 3.25.3, HHVM 3.24.7, and 3.21.11

These releases contain several bugfixes:

• CVE-2018-6335: potential DoS in Proxygen’s handling of HTTP2 header padding
• CVE-2018-5711: PHP Bug #75571: Potential infinite loop in gdImageCreateFromGifCtx()
• PHP Bug #73957: signed integer conversion in imagescale()
• CVE-2017-10989, CVE-2017-13685, CVE-2017-15286, CVE-2018-8740: multiple issues in SQLite

Additionally:

• several portability improvements have been backported to ease building LTS branches on MacOS
• we are now packaging 3.24 and 3.25 for Ubuntu 18.04 (Bionic Beaver)