GREEDY_REALLOC_APPEND: Make more type safe

Previously, GREEDY_REALLOC_APPEND would compile perfectly fine and cause
subtle memory corruption if the caller messes up the type they're passing
in (i.e. by forgetting to pass-by-reference when appending a Type* to an
array of Type*). Now this will lead to compilation failure

src/basic/alloc-util.h

@@ -155,7 +155,10 @@ void* greedy_realloc_append(void **p, size_t *n_p, const void *from, size_t n_fr
         greedy_realloc0((void**) &(array), (need), sizeof((array)[0]))
 
 #define GREEDY_REALLOC_APPEND(array, n_array, from, n_from)             \
-        greedy_realloc_append((void**) &(array), (size_t*) &(n_array), (from), (n_from), sizeof((array)[0]))
+        ({                                                              \
+                const typeof(*(array)) *_from_ = (from);                \
+                greedy_realloc_append((void**) &(array), &(n_array), _from_, (n_from), sizeof((array)[0])); \
+        })
 
 #define alloca0(n)                                      \
         ({                                              \