I'm assuming that the 'GridEntityCrossStencil' enum constant was cast to 1

This does not need any code in cmake as the macro is defined by the
compiler itself. See also the table here:
http://nadeausoftware.com/articles/2012/10/c_c_tip_how_detect_compiler_name_and_version_using_compiler_predefined_macros

Among other things, this shortens the output to the console and speeds
up the build.

For compatibility with unported examples, the old typedef is still kept,
but IndexType should be removed from grids eventually.

It was unused and pointless (use entity.getMeasure() instead).