clang: Update version from 4.0.1 to 6.0.0

[Release notes for 6.0.0][1] (excerpt):

> ### Non-comprehensive list of changes in this release ###
>
> *   Support for retpolines was added to help mitigate “branch target injection”
> (variant #2) of the “Spectre” speculative side channels described by Project
> Zero and the Spectre paper.
> *   Bitrig OS was merged back into OpenBSD, so Bitrig support has been removed
> from Clang/LLVM.
> *   The default value of _MSC_VER was raised from 1800 to 1911, making it
> compatible with the Visual Studio 2015 and 2017 C++ standard library headers.
> Users should generally expect this to be regularly raised to match the most
> recently released version of the Visual C++ compiler.
> *   clang now defaults to .init_array if no gcc installation can be found. If a
> gcc installation is found, it still prefers .ctors if the found gcc is older
> than 4.7.0.
> *   The new builtin preprocessor macros __is_target_arch, __is_target_vendor,
> __is_target_os, and __is_target_environment can be used to to examine the
> individual components of the target triple.

[1]: https://releases.llvm.org/6.0.0/tools/clang/docs/ReleaseNotes.html

clang.be0

@@ -1,6 +1,6 @@
 #!/usr/bin/env beesh
 
-# BEE_VERSION clang-4.0.1-0
+# BEE_VERSION clang-6.0.0-0
 
 ## this file was created by bee init and should be executed to build a
 ## bee-package. (Additional hints are located at the end of this file.)