external/boost: Avoid some -Wdeprecated-variadic-comma-omission

...new with GCC 15 trunk -std=c++26 since
<https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=cc67d95dc100706ea665e8cce581d59466aba62e>
"c++: Implement C++26 P3176R1 - The Oxford variadic comma",

> In file included from workdir/UnpackedTarball/boost/boost/rational.hpp:82,
>                  from source/external/boost/include/boost/rational.hpp:30,
>                  from source/tools/source/generic/fract.cxx:32:
> workdir/UnpackedTarball/boost/boost/integer/common_factor_rt.hpp:66:56: error: omission of ‘,’ before varargs ‘...’ is deprecated in C++26 [-Werror=deprecated-variadic-comma-omission]
>    66 |          inline constexpr void constexpr_swap(T&a, U& b...) BOOST_GCD_NOEXCEPT(T)
>       |                                                        ^~~
>       |                                                        ,

and

> In file included from workdir/UnpackedTarball/boost/boost/move/unique_ptr.hpp:24,
>                  from workdir/UnpackedTarball/boost/boost/spirit/home/classic/core/non_terminal/impl/grammar.ipp:18,
>                  from workdir/UnpackedTarball/boost/boost/spirit/home/classic/core/non_terminal/grammar.hpp:21,
>                  from workdir/UnpackedTarball/boost/boost/spirit/home/classic/core.hpp:42,
>                  from workdir/UnpackedTarball/boost/boost/spirit/home/classic.hpp:24,
>                  from workdir/UnpackedTarball/boost/boost/spirit/include/classic.hpp:11,
>                  from source/external/boost/include/boost/spirit/include/classic.hpp:30,
>                  from sdext/source/pdfimport/pdfparse/pdfparse.cxx:23:
> workdir/UnpackedTarball/boost/boost/move/detail/unique_ptr_meta_utils.hpp:500:39: error: omission of ‘,’ before varargs ‘...’ is deprecated in C++26 [-Werror=deprecated-variadic-comma-omission]
>   500 | struct is_unary_function_impl<R (*)(T0...)>
>       |                                       ^~~
>       |                                       ,

Change-Id: I56856e274a7c577c53d96343992bb79d4c3d602e
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/177730
Reviewed-by: Stephan Bergmann <stephan.bergmann@allotropia.de>
Tested-by: Jenkins

external/boost/0001-Add-a-comma-before-ellipsis-in-constexpr_swap.patch.2

@@ -0,0 +1,28 @@
+From 2dfe66886d71b9a341433ea8b6ff225cc07da80b Mon Sep 17 00:00:00 2001
+From: Andrey Semashev <andrey.semashev@gmail.com>
+Date: Mon, 2 Dec 2024 19:22:20 +0300
+Subject: Add a comma before ellipsis in constexpr_swap.
+
+gcc 15 complains that the comma is required before vararg ellipsis.
+
+Fixes https://github.com/boostorg/integer/issues/35.
+---
+ include/boost/integer/common_factor_rt.hpp | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/include/boost/integer/common_factor_rt.hpp b/include/boost/integer/common_factor_rt.hpp
+index d6765d4..817682f 100644
+--- a/include/boost/integer/common_factor_rt.hpp
++++ b/include/boost/integer/common_factor_rt.hpp
+@@ -64,7 +64,7 @@ namespace boost {
+             return a.swap(b);
+          }
+          template <class T, class U>
+-         inline constexpr void constexpr_swap(T&a, U& b...) BOOST_GCD_NOEXCEPT(T)
++         inline constexpr void constexpr_swap(T& a, U& b, ...) BOOST_GCD_NOEXCEPT(T)
+          {
+             T t(static_cast<T&&>(a));
+             a = static_cast<T&&>(b);
+-- 
+2.47.1
+

external/boost/0001-Avoid-Wdeprecated-variadic-comma-omission-with-GCC-1.patch.2

@@ -0,0 +1,38 @@
+From aa25af1928cc275537276c1a50e6ba49333a3aec Mon Sep 17 00:00:00 2001
+From: Stephan Bergmann <stephan.bergmann@allotropia.de>
+Date: Mon, 2 Dec 2024 19:06:25 +0100
+Subject: Avoid -Wdeprecated-variadic-comma-omission with GCC 15 trunk
+ -std=c++26
+
+...since
+<https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=cc67d95dc100706ea665e8cce581d59466aba62e>
+"c++: Implement C++26 P3176R1 - The Oxford variadic comma"
+---
+ include/boost/move/detail/unique_ptr_meta_utils.hpp | 4 ++--
+ 1 file changed, 2 insertions(+), 2 deletions(-)
+
+diff --git a/include/boost/move/detail/unique_ptr_meta_utils.hpp b/include/boost/move/detail/unique_ptr_meta_utils.hpp
+index 4c6aeb5..27154e0 100644
+--- a/include/boost/move/detail/unique_ptr_meta_utils.hpp
++++ b/include/boost/move/detail/unique_ptr_meta_utils.hpp
+@@ -497,7 +497,7 @@ struct is_unary_function_impl<R (*)(T0)>
+ {  static const bool value = true;  };
+ 
+ template <typename R, class T0>
+-struct is_unary_function_impl<R (*)(T0...)>
++struct is_unary_function_impl<R (*)(T0, ...)>
+ {  static const bool value = true;  };
+ 
+ #else // BOOST_MOVE_TT_TEST_MSC_FUNC_SIGS
+@@ -519,7 +519,7 @@ struct is_unary_function_impl<R (__cdecl*)(T0)>
+ {  static const bool value = true;  };
+ 
+ template <typename R, class T0>
+-struct is_unary_function_impl<R (__cdecl*)(T0...)>
++struct is_unary_function_impl<R (__cdecl*)(T0, ...)>
+ {  static const bool value = true;  };
+ 
+ #endif
+-- 
+2.47.1
+

external/boost/UnpackedTarball_boost.mk

@@ -36,6 +36,12 @@ boost_patches += Wundef.patch.0
 
 boost_patches += boost.spirit.noreturn.patch
 
+boost_patches += 0001-Add-a-comma-before-ellipsis-in-constexpr_swap.patch.2
+
+# Sent upstream as <https://github.com/boostorg/move/pull/58> "Avoid
+# -Wdeprecated-variadic-comma-omission with GCC 15 trunk -std=c++26":
+boost_patches += 0001-Avoid-Wdeprecated-variadic-comma-omission-with-GCC-1.patch.2
+
 $(eval $(call gb_UnpackedTarball_UnpackedTarball,boost))
 
 $(eval $(call gb_UnpackedTarball_set_tarball,boost,$(BOOST_TARBALL)))