buildworld build times 10-stable vs. 11-stable

[Dan Mack]

I have a system which builds world, kernel, install, boot, installworld, 
reboot several times per week.   I just noticed that my build times 
increased from about (just cherry picking a couple build logs):

   Starting build of FreeBSD SVN [309852]  10.3-STABLE
   Kernel will be GENERIC
     building world ... 	90:35 0


   Starting build of FreeBSD SVN [312099]  11.0-STABLE
   Kernel will be GENERIC
     building world ... 	146:23 0

before I start bisecting the log files, is there something obvious 
introduced in 11 that I missed that would explain the roughly 50 minute 
difference in my build times?   clang?  additional subsystems?

I'm using the same zpool / disks / memory etc.

Dan