I added the 1.27 PHP compatibility information (diff), though have not yet reviewed the existing information for accuracy. I have not added HHVM information because it is not clear what the minimum supported version of HHVM is; RELEASE-NOTES-1.27 is currently inconsistent on the matter.
This has happened in the meantime, comparing https://www.mediawiki.org/w/index.php?title=Compatibility&oldid=2014764#PHP to https://www.mediawiki.org/w/index.php?title=Compatibility&oldid=2219846#PHP
I made it happen, see above :)
As for HHVM, I just edited the page to mention the "experimental support" for it, though not a specific minimum version. (RELEASE-NOTES-1.28 states 3.6.5, though that may easily change.)