The following no-herd? ebuild no-herd: /usr/portage/sys-devel/llvm/llvm-2.7.ebuild build OK on alpha, request "~alpha" keyword. By the way, failed to build sys-devel/llvm-gcc-2.7{,-r1}; will fill another bug report after giving a closer look...
I thought bug #337018 was about llvm, but I did not read it fine, it is actually about llvm-gcc (so this already has a bug opened) llvm itself has a nice test suite also, to check if it works fine on your arch
Sorry, we currently lack the archtesting manpower to ensure speedy handling of such a large number of new packages.