libclc now has a build system

Hi all,

I have just committed new directory layout and build system for libclc.
The build system will build a builtins.bc for the ptx32 and ptx64
architectures. The script has also been updated to
cause test programs to link with builtins.bc (eventually this will
become part of the Clang driver).

Usage is:

./ --with-llvm-config=/path/to/llvm-config && make

You need a very recent LLVM/Clang (r143316 or later) for the script to work.