brew install p7zip isn't working anymore with macOS 10.13 and 10.12.
Let's use --build-from-source parameter with brew installation
Pick-to: 5.12.7
Task-number: QTQAINFRA-4128
Change-Id: Ib1a2db1cd3176955cca450e5ebe0d0fc1bee3aa4
Reviewed-by: Tony Sarajärvi <tony.sarajarvi@qt.io>