Explain that it affects only targets added after the call. Fix the link
to the COMPILE_OPTIONS directory propert documentation. Update the
latter to explain that it is used to initialize the corresponding target
property when a target is created.
Generator expressions are supported in many places and are a distinct
concept worthy of their own manual page. The old builtin documentation
was previously represented by preprocessor macros to generate it into
each place that supports them. Factor out the duplicate content into a
dedicated cmake-generator-expressions manual page and reference it from
each original location.
Brad King
Stephen Kelly
Kitware Robot