Help: Add 4.2 release note about VS flag suppression

Document flags suppressed by commit 7202539fd4 (VS: Suppress MSBuild
default flags not specified by project or user, 2025-09-10,
v4.2.0-rc1~188^2~1).

Help/release/4.2.rst

@@ -219,3 +219,8 @@ Other Changes
 * For builds targeting the MSVC ABI, all generators now add the ``_WINDLL``
   preprocessor definition when compiling sources in shared libraries.
   See policy :policy:`CMP0203`.
+
+* The :ref:`Visual Studio Generators` now suppress Visual Studio's default
+  flags ``-fp:precise``, ``-Gd``, and ``-GS`` if they are not specified by
+  the project or user.  This makes builds more consistent with other
+  generators, and with what projects and users actually specify.