clang on OS X

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

There seems to be significant progress regarding using clang as a pkgrsc 
compiler. Using pkgsrc on OS X, that makes my life easier, thanks.

However, I regularily run into some packages not building because of clang 
being pickier about possible programming errors (see pkg/48318 for an example), 
or other issues, the weirdest one so far being
        fatal error: error in backend: Unsupported asm: input constraint with a 
matching output constraint of incompatible type!
in x11/pixman.

The clang I'm using is
        Apple clang version 1.7 (tags/Apple/clang-77) (based on LLVM 2.9svn)
while pkgsrc contains a 3.3 one.

So two questions on the subject:
1. Does anyone run bulk builds with clang?
   If yes, on which platform using which clang version?
2. What's the suggested/supported way using clang/OS X?
   Use the clang that comes with Xcode or build clang from pkgsrc?