[gentoo-alt] Prefix on Sierra: ObjC broken with clang-3.8

[Michael Weiser <michael@weiser.dinsnail.net>]

Hey guys,

is anyone running prefix on Sierra yet?

I am and I've had only one but majorish problem getting it to work:
Everything containing Objective-C code (gtk, dev-scheme/guile, git,
glib, lbdb) failed to compile with clang 3.8. The errors all were like
this:

In file included from /usr/local/gentoo/var/tmp/portage/x11-libs/gtk+-2.24.31-r1/work/gtk+-2.24.31/gdk/quartz/GdkQuartzView.c:21:
In file included from /usr/local/gentoo/var/tmp/portage/x11-libs/gtk+-2.24.31-r1/work/gtk+-2.24.31/gdk/quartz/GdkQuartzView.h:21:
In file included from /System/Library/Frameworks/AppKit.framework/Headers/AppKit.h:10:
In file included from /System/Library/Frameworks/Foundation.framework/Headers/Foundation.h:10:
In file included from /System/Library/Frameworks/Foundation.framework/Headers/NSArray.h:5:
/System/Library/Frameworks/Foundation.framework/Headers/NSObject.h:44:12:
error: unknown property attribute 'class'
@property (class, readonly) BOOL supportsSecureCoding;
           ^

On a hunch that Apple once again started using new language constructs
in the system headers as soon as they became available in their latest
Xcode clang I've hacked the llvm-3.9.0 ebuild to install a working
clang-3.9 and lo and behold all the stuff that failed before compiled
and installed fine.

Did anyone else observe this behaviour or is something screwed up on my
system?

BTW: That system was a fresh install of El Capitan with Xcode 8 which I
upgraded just a few days later to Sierra. I manually updated the Xcode
command line tools to 8.0 for Sierra via the .pkg from
developer.apple.com.

Another way might have been to downgrade Xcode to possibly get the older
system headers as well but I didn't try that. (The way out is forward. ;)
-- 
Thanks,
Michael