sys-apps/systemd: add v256.5 with musl libc patches

- https://code.atwilcox.tech/sphen/scaly/systemd
- https://catfox.life/2024/09/05/porting-systemd-to-musl-libc-powered-linux/

sys-apps/systemd/files/0026-basic-Add-needed-signal.h-to-pidref.h.patch

@@ -0,0 +1,28 @@
+From c4425b22e47569dd79b611b641de9e1b1a3630b8 Mon Sep 17 00:00:00 2001
+From: "A. Wilcox" <AWilcox@Wilcox-Tech.com>
+Date: Sun, 18 Aug 2024 03:14:44 -0500
+Subject: [PATCH 26/34] basic: Add needed <signal.h> to pidref.h
+Content-Type: text/plain; charset="utf-8"
+Content-Transfer-Encoding: 8bit
+
+Signed-off-by: A. Wilcox <AWilcox@Wilcox-Tech.com>
+Signed-off-by: Alexander Miroshnichenko <alex@millerson.name>
+---
+ src/basic/pidref.h | 1 +
+ 1 file changed, 1 insertion(+)
+
+diff --git a/src/basic/pidref.h b/src/basic/pidref.h
+index 9920ebb9b3bc..2fdd4ff50f8f 100644
+--- a/src/basic/pidref.h
++++ b/src/basic/pidref.h
+@@ -1,6 +1,7 @@
+ /* SPDX-License-Identifier: LGPL-2.1-or-later */
+ #pragma once
+ 
++#include <signal.h>
+ #include "macro.h"
+ 
+ /* An embeddable structure carrying a reference to a process. Supposed to be used when tracking processes continuously. */
+-- 
+2.41.0
+