Rollup merge of #64618 - alexcrichton:improve-dist-output, r=Mark-Simulacrum
Rollup merge of #64618 - alexcrichton:improve-dist-output, r=Mark-Simulacrum

rustbuild: Improve output of `dist` step

* Pass `/Q` to `iscc` on Windows to supress the thousands of lines of
  output about compressing documentation.
* Print out what's happening before long steps
* Use `timeit` to print out timing information for long-running
  installer assemblies.
* Try to scope output of `Dist ...` to not also encompass actual build steps

graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust