Please don't try to use Xcode 7 on 10.12. Compiling almost anything will fail in fun ways. Install the Xcode 8 beta or the 8.x CLT package & ensure you've pointed sudo xcode-select --switch at either one.

Like Christmas, once a year a new operating system for Macs swings around... and like Christmas a bunch of toys get broken accidentally. This year's broken toys include:

Broken:

• Qt: https://gist.github.com/anonymous/e19027178831fd17d2e17a9bf65ead02 - Fails to find a header, which does still exist on 10.12, so a bit puzzling. We're migrating things to Qt5 any way, so Qt may not be supported by us on 10.12.
• haskell-stack: https://gist.github.com/8e005710eab17139c02267bac3029e33 - Confusing compiler error. Upstream report: https://ghc.haskell.org/trac/ghc/ticket/12198
• guile: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=23870 - more clock_gettime fun.

Upstream/Homebrew 10.12 support hacks:

• libgcrypt: https://gist.github.com/anonymous/5a60bffda24503a6f478c0c6baa2594a - make check dies, we saw something similar when El Cap came out so not a big surprise. Hacked a solution in 8311571 temporarily.
• wxmac: wxmac fails to build on OSX 10.12 #1996, https://gist.github.com/anonymous/5d22977c76e44ffd920a99ba0ec061ec - --devel works, patch is too big to backport to stable.

Resolved:

• perl: https://gist.github.com/mistydemeo/37cb3474a09c51b7356683a31b41352b - Looks like another time bug. Has been patched in the formula.
• tor: https://gist.github.com/mistydemeo/6bc4f2fc724ee0c2b9ba86205c431aef - Another time-related bug, assumes another function is available if clock_gettime is. Upstream patch was merged into latest release.
• libevent: libevent: [warn] kq_init: detected broken kqueue; not using.: Undefined error: 0 #2869 - Marked fixed by upstream & patch backported to formula.
• go - Fixed by Go 1.7's release.

Just so people are aware: Comments highlighting issues that turn out not to be actual formulae issues, i.e. user configuration problems, will be chopped after a couple of days to keep this thread from getting drowned.