Help/OPTIMIZE_DEPENDENCIES: xref with CMP0154 documentation

Closes: #27250

Help/policy/CMP0154.rst

@@ -20,7 +20,8 @@ their own target by default.  Generated public headers must be specified
 as members of a ``PUBLIC`` (or ``INTERFACE``) ``FILE_SET``, typically of
 type ``HEADERS``.  With this information, :ref:`Ninja Generators` may omit
 the above-mentioned conservative dependencies and produce more efficient
-build graphs.
+build graphs.  Dependents to such targets may also prune dependencies to such
+targets when using the :prop_tgt:`OPTIMIZE_DEPENDENCIES` target property.
 
 Additionally, if the custom command's output is a member of a file set of type
 ``CXX_MODULES``, it will additionally not be required to exist before

Help/prop_tgt/OPTIMIZE_DEPENDENCIES.rst

@@ -21,7 +21,9 @@ any of the following criteria:
 * The dependency has any ``PRE_BUILD``, ``PRE_LINK``, or ``POST_BUILD`` custom
   commands associated with it.
 * The dependency contains any source files that were generated by a custom
-  command.
+  command. However, if :policy:`CMP0154` is `NEW` for the dependency and it
+  uses :ref:`File Sets`, only source files that are not in a ``PUBLIC``,
+  ``INTERFACE``, or of type ``CXX_MODULES`` are considered.
 * The dependency contains any languages which produce side effects that are
   relevant to the library. Currently, all languages except C, C++, Objective-C,
   Objective-C++, assembly, and CUDA are assumed to produce side effects.