[Release] Allow release testers to disable certain components

[Release] Allow release testers to disable certain components

Not all components build correctly on all targets and the release
script had no way to disable them other than editing the script locally.

This change provides a way to disable the test-suite, compiler-rt and
the libraries, as well as allowing you to re-run on the same directory
without checking out all sources again.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@242919 91177308-0d34-0410-b5e6-96231b3b80d8