How to use an alternate toolset in rpmbuild

I am trying to compile & package the latest version of Zeek (5.0.7) for rhel 7 servers. I get an error saying the "cxx17" is required. Searching the web, I found that it is contained in devtoolset-7 which I downloaded. However, I can't find anything telling me what I have to put in the spec file for it to be used.