Add documented patch series and build instructions

patches/0004-Add-missing-headers-for-modern-toolchains.patch

@@ -0,0 +1,51 @@
+From 8f89723b4f32c3ce70dbb3f99f1c176e4492692d Mon Sep 17 00:00:00 2001
+From: Christoph <ckubu@oopen.de>
+Date: Sun, 14 Dec 2025 11:49:29 +0100
+Subject: [PATCH 4/4] Add missing headers for modern toolchains
+
+---
+ src/dmail/dmail.c | 1 +
+ src/mlock/mlock.c | 2 ++
+ src/tmail/tmail.c | 1 +
+ 3 files changed, 4 insertions(+)
+
+diff --git a/src/dmail/dmail.c b/src/dmail/dmail.c
+index f78b957..b569c16 100644
+--- a/src/dmail/dmail.c
++++ b/src/dmail/dmail.c
+@@ -35,6 +35,7 @@ extern int errno;		/* just in case */
+ #include <sys/stat.h>
+ #include "c-client.h"
+ #include "dquota.h"
++#include <ctype.h>
+ 
+ 
+ /* Globals */
+diff --git a/src/mlock/mlock.c b/src/mlock/mlock.c
+index 1dca40e..95f3729 100644
+--- a/src/mlock/mlock.c
++++ b/src/mlock/mlock.c
+@@ -40,6 +40,8 @@
+ #include <netdb.h>
+ #include <ctype.h>
+ #include <string.h>
++#include <unistd.h>   /* write, read, close, link, unlink, chdir, sleep, getpid, gethostname */
++#include <time.h>     /* time */
+ 
+ #define LOCKTIMEOUT 5		/* lock timeout in minutes */
+ #define LOCKPROTECTION 0664
+diff --git a/src/tmail/tmail.c b/src/tmail/tmail.c
+index ed5fc58..95ecbd2 100644
+--- a/src/tmail/tmail.c
++++ b/src/tmail/tmail.c
+@@ -35,6 +35,7 @@ extern int errno;		/* just in case */
+ #include <sys/stat.h>
+ #include "c-client.h"
+ #include "tquota.h"
++#include <ctype.h>
+ 
+ 
+ /* Globals */
+-- 
+2.47.3
+