[libc++] [ABI BREAK] Conform lognormal_distribution::param_type.

Fixes #52906.

Differential Revision: https://reviews.llvm.org/D116344

NOKEYCHECK=True
GitOrigin-RevId: 0359b85c61b54354949a68f41a6881fb15f1c22b
diff --git a/docs/ReleaseNotes.rst b/docs/ReleaseNotes.rst
index 1a8c007..4a18312 100644
--- a/docs/ReleaseNotes.rst
+++ b/docs/ReleaseNotes.rst
@@ -119,6 +119,15 @@
   constructing a ``std::random_device`` will now be ignored instead of interpreted as a
   file to read entropy from.
 
+- ``std::lognormal_distribution::param_type`` used to store a data member of type
+  ``std::normal_distribution``; now this member is stored in the ``lognormal_distribution``
+  class itself, and the ``param_type`` stores only the mean and standard deviation,
+  as required by the Standard. This changes ``sizeof(std::lognormal_distribution::param_type)``.
+  You can define the ``_LIBCPP_ABI_OLD_LOGNORMAL_DISTRIBUTION`` macro to return to the
+  previous behavior. That macro will be removed in LLVM 15. Please comment
+  `here <https://llvm.org/PR52906>`_ if you are broken by this change and need to
+  define the macro.
+
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