$ rpmbuild --showrc
The definition for %cmake is quite long, but includes this line: %{!?__cmake_in_source_build:-B "%{__cmake_builddir}"} \
%__cmake_builddir is defined as: %{!?__cmake_in_source_build:%{_vpath_builddir}}%{?__cmake_in_source_build:.}
And then %_vpath_builddir is defined as: %{_vendor}-%{_target_os}-build
So that's where "redhat-linux-build" comes from.
A.FI.