[gentoo-user] ebuild for "gcc-independent llvm and clang for linux"

[やまぐちたかゆき]

Hello everybody,

I'm going to build and install llvm and clang packages in my "Linux" PC as
1. Binaries of llvm and claag installed finally were compiled by clang.
2. The binaries of 1. depend on libc++.so instead of libstdc++.so.
3. libc++.so was installed by portage.
4. The binaries of llvm, clang, and libc++.so are not linked with libgcc.