[CMake] Immutable variables?

[Orion Poplawski]

I ran across a project that set CMAKE_SOURCE_DIR/CMAKE_BINARY_DIR.  This is a
really bad idea, but apparently used to work for their use case.  With cmake
3.5 this no longer works, but was somewhat hard to track down.

I'm wondering if is makes to be able to mark cmake generated variables as
immutable and error out if they are attempted to be set.  Thoughts?

-- 
Orion Poplawski
Technical Manager                     303-415-9701 x222
NWRA, Boulder/CoRA Office             FAX: 303-415-9702
3380 Mitchell Lane                       orion at nwra.com
Boulder, CO 80301                   http://www.nwra.com