Connect LLVM CMake build scripts to LLDB's CMake scripts:

- if you have LLDB checked out in $llvm/tools, CMake will build it now!
- LLDB is known to build on Linux with libstdc++ and GCC 4.6/4.7 or Clang 3.3
- to run lldb tests, do "make check-lldb" after a build

llvm-svn: 176307