main-func: Reduce transitive includes

Let's move some logic from _DEFINE_MAIN_FUNCTION() and other places
in main-func.h into functions that we implement in main-func.c to
allow moving some included headers from the header to the .c file.

src/rfkill/rfkill.c

@@ -12,6 +12,7 @@
 
 #include "alloc-util.h"
 #include "device-util.h"
+#include "errno-util.h"
 #include "escape.h"
 #include "fd-util.h"
 #include "fileio.h"