[cfe-dev] Small patches to allow fully independent clang/llvm/compiler-rt/libc++

[Vasileios Kalintiris via cfe-dev]

> Some people may disagree on the principle, even if it doesn't affect
> current builds. But I'll let them voice their concerns.

IMHO, the "correct" approach for a GNU-free/independent clang package requires
a new ToolChain class for LLVM-based toolchains. Maybe, this class could
inherit from the Linux ToolChain and use most of the existing infrastructure
for paths, options & tools invocations. Otherwise, we could use these
configuration-time options for most of the GNU-dependencies that we want to
replace. However, I think that we would be duplicating effort/functionality
at two different places (cmake & clang source code). Additionally, other than
compiler-rt, libcxx, libcxxabi, etc., we'd need a non-GLIBC/GNU C library
which might have a different set of CRT files with its own naming scheme for the
dynamic linker/loader.

Having said all that, I don't explicitly disagree with these set of patches.
They could offer a reasonable trade-off for the time being.

- Vasileios