Merge topic 'process-refactor'

d6111df5cb cmUVStream: Remove unused cmUVPipeIStream
c94d70c345 cmUVProcessChain: Open output streams automatically
ca0e9418f3 cmUVProcessChain: Simplify representation of merged streams
38ee29a66a cmUVProcessChain: Build stdout before stderr
ca0ba19d6d cmUVStream: Fix cmUVIStream constructor compilation with legacy XL compiler
5f54ad41e7 cmCTestScriptHandler: De-duplicate WaitForLine call
6f5bbf9ee7 cmSystemTools: Remove unused timeout argument from WaitForLine

Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !11532