Update the wording of some examples to avoid long lines in code blocks.
Otherwise the formatted documentation can exceed certain column width
limitations.
The DECL part is redundant, and the language part is not needed. The
source language and context already determines the language, so there
is no need to repeat it in the define name.
Link to it from the documentation of related properties, variables
and commands.
Extend the cmake-developer(7) documentation with notes on
extending feature support for compilers.
David Demelier
Brad King
Stephen Kelly