They have actually fixed it - if you get bit with it then you can reference rdar://problem/22242515
The WebKit bug is here:
https://bugs.webkit.org/show_bug.cgi?format=multiple&id=1528...
The patch to fix it is here:
https://bugs.webkit.org/attachment.cgi?id=268394&action=diff
The workaround, FWIW (thanks Simon!) is to add shrink-to-fit=no” to the meta viewport tag.
For me, it was too much effort to get OpenGrok fixed, so I just did a rewrite rule in Charles Proxy that gets rid of the style attribute.
I reported it in October and Apple's security team replied they're aware of it but it's still not fixed 2 releases later even though they probably need to fix like 1 line of code (the advertised version flag).