Bug#907269: llvm-defaults: Add clang-diff tool

[Marco F]

Source: llvm-defaults
Version: 0.42exp1
Severity: wishlist

clang-diff is a new tool in clang-6.0 [1], however I couldn't install
it with the package manager [2]. Note that other tools, for example,
clang-format (1:6.0-42exp1) can be installed with the package
manager [3].

So please consider adding the new tool clang-diff.

--Marco

[1] https://github.com/llvm-mirror/clang/tree/release_60/tools/clang-diff
[2] https://packages.debian.org/experimental/clang-diff
[3] https://packages.debian.org/experimental/clang-format