COMP: Pass CMAKE_BUILD_TYPE to external project for all configurations

Thanks to Hans Johnson <hans-johnson@uiowa.edu> for reporting the problem.

Before this commit, CMAKE_BUILD_TYPE was passed to external project only
the first configuration if it wasn't already defined (by passing -D option).

Co-authored-by: Hans Johnson <hans-johnson@uiowa.edu>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22797 3bd1e089-480b-0410-8dfb-8563597acbee