missing llvm-windres alias

[vszakats at gmail.com]

Dear LLVM Packaging Team,

In debian:testing / debian:unstable, the llvm package misses 
llvm-windres. [1] This should be a symlink to llvm-rc, making 
it behave as a replacement for the windres tool in binutils-mingw-w64.

I run into this after switching a Windows cross-build over to 
use LLVM tools with clang, and this one binary turned out to
be missing when run on debian:testing.

I'm glad to respond if you have any questions.

[1] https://packages.debian.org/unstable/amd64/llvm/filelist

Kind regards,
Viktor