I'm now checking out the boost-1.64.0 tag to see how it would fare.
boost-1.64.0 fails as well.
Mystery solved, the changes that fixed clang are not in 1.64.
C:\Projects\boost-git\boost\libs\preprocessor>git log boost-1.64.0..master
commit b19e4deacb7103061f9c2c9efcdd77eaa5877df0
Merge: a627594 dfc1c46
Author: Edward Diener
Date: Mon Apr 24 12:13:09 2017 -0400
Merge branch 'develop'
commit dfc1c46ecedef21274eb142e267e91400aa33ec8
Author: Edward Diener
Date: Sun Mar 26 08:51:41 2017 -0700
With _MSC_VER and __clang__ always use strict mode and variadics turned
on w
commit e474eea44f00ba92310ace20add3956adb83f3de
Author: Edward Diener
Date: Sun Mar 26 01:02:05 2017 -0700
Slight correction to particularize previous change as involving
only -fno-ms
commit b03c6cd3c0f855f22f154424272ef9276ed72594
Author: Edward Diener
Date: Sat Mar 25 23:22:32 2017 -0700
In the configuration the combination of clang defined and gcc defined
always
