Support stamp in run_binary

[tpudlik]

It's common to use genrule with stamp = -1 to integrate the workspace status (git hash or timestamp) into binaries. (This is not well documented, but see bazelbuild/bazel#4942.) However, genrule is not cross-platform; folks should really be using run_binary instead of genrule wherever they can. Unfortunately, run_binary doesn't have the stamp attribute!

The FR is to add that support.

BTW, the bazel-lib fork of run_binary does support stamp = -1 bazel-contrib/bazel-lib#185. I'm not sure if the fork is close enough for the support to be easy to upstream.