Remove unneeded loop through size_pools

This function loops twice through the array of size pools. Once to set
up the pages list, and then again later on in the function to set the
allocatable_pages count.

We don't do anything with the size pools in between the invocation of
these loops that will affect the size pools, so this commit removes the
second loop and moves the allocatable_pages count update into the first
loop.

gc.c

@@ -3527,6 +3527,11 @@ rb_gc_impl_objspace_alloc(void)
         rb_bug("Could not preregister postponed job for GC");
     }
 
+    // TODO: debug why on Windows Ruby crashes on boot when GC is on.
+#ifdef _WIN32
+    dont_gc_on();
+#endif
+
     for (int i = 0; i < SIZE_POOL_COUNT; i++) {
         rb_size_pool_t *size_pool = &size_pools[i];
 
@@ -3534,15 +3539,14 @@ rb_gc_impl_objspace_alloc(void)
 
         ccan_list_head_init(&SIZE_POOL_EDEN_HEAP(size_pool)->pages);
         ccan_list_head_init(&SIZE_POOL_TOMB_HEAP(size_pool)->pages);
+
+        gc_params.size_pool_init_slots[i] = GC_HEAP_INIT_SLOTS;
+
+        size_pool->allocatable_pages = minimum_pages_for_size_pool(objspace, size_pool);
     }
 
     rb_darray_make(&objspace->weak_references, 0);
 
-    // TODO: debug why on Windows Ruby crashes on boot when GC is on.
-#ifdef _WIN32
-    dont_gc_on();
-#endif
-
 #if defined(INIT_HEAP_PAGE_ALLOC_USE_MMAP)
     /* Need to determine if we can use mmap at runtime. */
     heap_page_alloc_use_mmap = INIT_HEAP_PAGE_ALLOC_USE_MMAP;
@@ -3556,15 +3560,6 @@ rb_gc_impl_objspace_alloc(void)
     objspace->rgengc.oldmalloc_increase_limit = gc_params.oldmalloc_limit_min;
 #endif
 
-    /* Set size pools allocatable pages. */
-    for (int i = 0; i < SIZE_POOL_COUNT; i++) {
-        rb_size_pool_t *size_pool = &size_pools[i];
-
-        /* Set the default value of size_pool_init_slots. */
-        gc_params.size_pool_init_slots[i] = GC_HEAP_INIT_SLOTS;
-
-        size_pool->allocatable_pages = minimum_pages_for_size_pool(objspace, size_pool);
-    }
     heap_pages_expand_sorted(objspace);
 
     init_mark_stack(&objspace->mark_stack);