Installing LLVM/Clang/LLDB 3.4 on RHEL 6.2

The lab I work for uses RHEL 6.2; this means the versions of GNU
compilers and libraries such as libc that came with the OS are too old
to use newer C++; this is also a problem when trying to build LLDB
because it can't find <atomic>.

We don't really need to use GCC as far as I can tell; we should be
able to use libc++, libc++abi and libc++rt and avoid using GCC at all,
right? With that said, we have several newer versions of GCC (4.6,
4.7.2 and 4.8.2) installed to alternative locations; I'm just not sure
how to hook them up when building LLVM/Clang and couldn't find build
options for it.

tl;dr Is there documentation somewhere on how to build LLVM/Clang/LLDB
without using libstdc and libstdc++?

tl;dr Is there documentation somewhere on how to build LLVM/Clang/LLDB
without using libstdc and libstdc++?

AFAIK the usual way of doing this is to pass the CXX and CC environment variables to CMake or the configure script.

CMake