opensmtpd: patch another usage of PATH_LIBEXEC (#503259)

- `light` has been removed because it was unmaintained.

  `brightnessctl` and `acpilight` provide similar functionality.

- `opensmtpd-filter-dkimsign` is now installed into `libexec/smtpd` instead of `libexec/opensmtpd` so that now it is properly linked into the environment built by `services.opensmtpd.procPackages`. If you hardcoded path to `filter-dkimsign` please consider using this option.

- `services.openssh.settings.AcceptEnv` now explicitly defined as an option that takes a list of strings, to facilitate option merging. Setting it to a string value is no longer supported.

- All Xfce packages have been moved to top level (e.g. if you previously added `pkgs.xfce.xfce4-whiskermenu-plugin` to `environment.systemPackages`, you will need to change it to `pkgs.xfce4-whiskermenu-plugin`). The `xfce` scope will be removed in NixOS 26.11.

diff --git a/usr.sbin/smtpd/smtpd.c b/usr.sbin/smtpd/smtpd.c

index e049f07c..a1bd03a0 100644

index 2365b1ee..b1b6bcec 100644

--- a/usr.sbin/smtpd/smtpd.c

+++ b/usr.sbin/smtpd/smtpd.c

@@ -1157,6 +1157,7 @@ fork_proc_backend(const char *key, const char *conf, const char *procname)

@@ -1224,6 +1224,7 @@ fork_proc_backend(const char *key, const char *conf, const char *procname,

 	char		path[PATH_MAX];

 	char		name[PATH_MAX];

 	char		*arg;

 	if (strlcpy(name, conf, sizeof(name)) >= sizeof(name)) {

 		log_warnx("warn: %s-proc: conf too long", key);

@@ -1167,7 +1168,12 @@ fork_proc_backend(const char *key, const char *conf, const char *procname)

@@ -1234,7 +1235,12 @@ fork_proc_backend(const char *key, const char *conf, const char *procname,

 	if (arg)

 		*arg++ = '\0';

 	    (ssize_t)sizeof(path)) {

 		log_warn("warn: %s-proc: exec path too long", key);

 		return (-1);

@@ -1387,6 +1393,7 @@ fork_filter_process(const char *name, const char *command, const char *user, con

 	int		 sp[2], errfd[2];

 	struct passwd	*pw;

 	struct group	*gr;

+	char		*proc_path;

 	char		 exec[_POSIX_ARG_MAX];

 	int		 execr;

@@ -1455,8 +1462,12 @@ fork_filter_process(const char *name, const char *command, const char *user, con

 	if (command[0] == '/')

 		execr = snprintf(exec, sizeof(exec), "exec %s", command);

 	else

+		proc_path = getenv("OPENSMTPD_PROC_PATH");

+		if (proc_path == NULL) {

+			proc_path = PATH_LIBEXEC;

+		}

 		execr = snprintf(exec, sizeof(exec), "exec %s/%s", 

-		    PATH_LIBEXEC, command);

+		    proc_path, command);

 	if (execr >= (int) sizeof(exec))

 		fatalx("%s: exec path too long", name);

diff --git a/usr.sbin/smtpd/table.c b/usr.sbin/smtpd/table.c

index 9cfdfb99..24dfcca4 100644

index e62b47af..2ee186bf 100644

--- a/usr.sbin/smtpd/table.c

+++ b/usr.sbin/smtpd/table.c

@@ -201,6 +201,7 @@ table_create(const char *backend, const char *name, const char *tag,

@@ -229,17 +229,23 @@ table_create(struct smtpd *conf, const char *backend, const char *name,

 	struct table		*t;

 	struct table_backend	*tb;

 	char			 buf[LINE_MAX];

 	char			 path[LINE_MAX];

+	const char		*proc_path;

 	size_t			 n;

 	struct stat		 sb;

@@ -215,11 +216,16 @@ table_create(const char *backend, const char *name, const char *tag,

 	if (name && table_find(name, NULL))

 	if (name && table_find(conf, name))

 		fatalx("table_create: table \"%s\" already defined", name);

+	proc_path = getenv("OPENSMTPD_PROC_PATH");