Add limited tmpfiles.d(5) support

This change adds very basic tmpfiles.d/ support to Finit.  Much of the
basic types are supported, but not all, so for now, please check the
code for details on what is working.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/tmpfiles.h

@@ -0,0 +1,42 @@
+/* Limited tmpfiles.d implementation
+ *
+ * Copyright (c) 2023  Joachim Wiberg <troglobit@gmail.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#ifndef TMPFILES_H_
+#define TMPFILES_H_
+
+#include <dirent.h>
+#include <ftw.h>
+#include <glob.h>
+#include <libgen.h>
+
+#include <stdlib.h>
+#include <string.h>
+#ifdef _LIBITE_LITE
+# include <libite/lite.h>
+#else
+# include <lite/lite.h>
+#endif
+
+void tmpfilesd(void);
+
+#endif /* TMPFILES_H_ */