IWYU update

- Add Settings forward declaration in Process.h
- Add assert.h include in XUitls.c
- Add conditional stdbool.h include in Object.h
- Drop unneeded stddef.h include in Richstring.c
- Drop unneeded unistd.h include in Process.h
- Drop unneeded string.h include in linux/Platform.c
- Use String_eq to avoid string.h include in Action.c
- Improve script to run custom iwyu version

Object.h

@@ -11,6 +11,10 @@ in the source distribution for its full text.
 #include "RichString.h"
 #include "XUtils.h" // IWYU pragma: keep
 
+#ifndef NDEBUG
+#include <stdbool.h>
+#endif
+
 
 struct Object_;
 typedef struct Object_ Object;