[libcxx] r243503 - [libcxx] Cleanup CMake configuration and integrate with LLVM

[Hans Wennborg]

I've reverted this in r243550 as it caused PR24306.

On Tue, Jul 28, 2015 at 5:03 PM, Eric Fiselier <eric at efcs.ca> wrote:
> Author: ericwf
> Date: Tue Jul 28 19:03:51 2015
> New Revision: 243503
>
> URL: http://llvm.org/viewvc/llvm-project?rev=243503&view=rev
> Log:
> [libcxx] Cleanup CMake configuration and integrate with LLVM
>
> Summary:
> This patch contains the following changes:
>
> 1. Require that libc++ can find a LLVM source directory. This is done the same way as `libc++abi` currently does.
> 2. Cleanup ugly configuration code in CMakeLists.txt by using `add_flags`, `add_flags_if`, and `add_flags_if_supported` macros.
>
> The goals for this patch are:
>
> 1. Help libc++ be more consistent with how LLVM handles CMake options (see PR23670 PR23671).
> 2. Make it easier to use sanitizers using the `LLVM_USE_SANITIZER` option.
> 3. Make libc++'s CMakeLists.txt file easier to understand and change.
> 4. Move towards allowing libc++ to create Sphinx documentation (see http://efcs.ca/libcxx-docs).
> 5. Move towards allowing  libc++ to use other LLVM utilities such as `not` and `FileCheck`.
>
>
>
> Reviewers: mclow.lists, jroelofs, danalbert
>
> Subscribers: cfe-commits
>
> Differential Revision: http://reviews.llvm.org/D11308