ref-manual: document BUILD_REPRODUCIBLE_BINARIES

(From yocto-docs rev: 9855ed9b35acede2f6e56509709000796a3927f3)

Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/migration-guides/migration-3.4.rst

@@ -243,7 +243,7 @@ Miscellaneous
   re-enable it, set ``AVAHI_GTK = "gtk3"`` in a bbappend for the
   ``avahi`` recipe or in your custom distro configuration file.
 
-- Setting the ``BUILD_REPRODUCIBLE_BINARIES`` variable to "0" no longer
+- Setting the :term:`BUILD_REPRODUCIBLE_BINARIES` variable to "0" no longer
   uses a strangely old fallback date of April 2011, it instead disables
   building reproducible binaries as you would logically expect.
 

documentation/ref-manual/variables.rst

@@ -906,6 +906,19 @@ system and gives an overview of their function and contents.
       :term:`TARGET_PREFIX` when building for
       ``native`` recipes.
 
+   :term:`BUILD_REPRODUCIBLE_BINARIES`
+      This variable allows the image building classes and recipes to produce
+      :ref:`reproducible binaries <test-manual/reproducible-builds:reproducible builds>`
+
+      If you inherit the
+      :ref:`reproducible-build <ref-classes-reproducible-build>` class,
+      which is the case of the Poky reference distribution, this sets this
+      variable to "1".
+
+      If your build inherits this classs but you wish to disable reproducible
+      binary generation for specific packages or images, you can set this
+      variable to "0" in the corresponding recipes.
+
    :term:`BUILD_STRIP`
       Specifies the command to be used to strip debugging symbols from
       binaries produced for the build host. By default, :term:`BUILD_STRIP`