Add previous commit as diff in patches/

Author: eddelbuettel

ChangeLog

@@ -1,3 +1,11 @@
+2026-10-06  Dirk Eddelbuettel  <edd@debian.org>
+
+	* patches/eigen-5.0.1-stan.diff: Document previous commit as diff
+
+2026-10-01  Dirk Eddelbuettel  <edd@debian.org>
+
+	* inst/include/Eigen/src/Core/Fill.h: Apply patch to aid StanHeaders
+
 2026-07-27  Dirk Eddelbuettel  <edd@debian.org>
 
 	* configure.ac: Conditionally adding compilation flags

patches/eigen-5.0.1-stan.diff

@@ -0,0 +1,17 @@
+diff --git o/inst/include/Eigen/src/Core/Fill.h w/inst/include/Eigen/src/Core/Fill.h
+index 779ef26..6f45935 100644
+--- o/inst/include/Eigen/src/Core/Fill.h
++++ w/inst/include/Eigen/src/Core/Fill.h
+@@ -93,8 +93,10 @@ struct eigen_fill_impl<Xpr, /*use_fill*/ true> {
+ 
+ template <typename Xpr>
+ struct eigen_memset_helper {
+-  static constexpr bool value =
+-      std::is_trivially_copyable<typename Xpr::Scalar>::value && eigen_fill_helper<Xpr>::value;
++  using Scalar = typename Xpr::Scalar;
++  static constexpr bool value = std::is_trivially_copyable<Scalar>::value &&
++                                !static_cast<bool>(NumTraits<Scalar>::RequireInitialization) &&
++                                eigen_fill_helper<Xpr>::value;
+ };
+ 
+ template <typename Xpr>