Help: Explicitly note that projects should not set CMAKE_CUDA_HOST_COMPILER

Issue: #25093

Help/variable/CMAKE_CUDA_HOST_COMPILER.rst

@@ -24,6 +24,13 @@ is read-only and changes to it are undefined behavior.
   it does not make sense to set ``CMAKE_CUDA_HOST_COMPILER`` without also
   setting ``CMAKE_CUDA_COMPILER`` to NVCC.
 
+.. note::
+
+  Projects should not try to set ``CMAKE_CUDA_HOST_COMPILER`` to match
+  :variable:`CMAKE_CXX_COMPILER <CMAKE_<LANG>_COMPILER>` themselves.
+  It is the end-user's responsibility, not the project's, to ensure that
+  the C++ and CUDA compilers target the same ABI.
+
 .. note::
 
   Ignored when using :ref:`Visual Studio Generators`.