gh-117755: Fix mimalloc for huge allocation on s390x (#117809)

Fix mimalloc allocator for huge memory allocation (around
8,589,934,592 GiB) on s390x.

Abort allocation early in mimalloc if the number of slices doesn't
fit into uint32_t, to prevent a integer overflow (cast 64-bit
size_t to uint32_t).

Misc/NEWS.d/next/Core and Builtins/2024-04-12-12-28-49.gh-issue-117755.6ct8kU.rst

@@ -0,0 +1,2 @@
+Fix mimalloc allocator for huge memory allocation (around 8,589,934,592 GiB) on
+s390x. Patch by Victor Stinner.

Objects/mimalloc/segment.c

@@ -814,6 +814,9 @@ static mi_segment_t* mi_segment_os_alloc( size_t required, size_t page_alignment
     const size_t extra = align_offset - info_size;
     // recalculate due to potential guard pages
     *psegment_slices = mi_segment_calculate_slices(required + extra, ppre_size, pinfo_slices);
+
+    // mi_page_t.slice_count type is uint32_t
+    if (*psegment_slices > (size_t)UINT32_MAX) return NULL;
   }
 
   const size_t segment_size = (*psegment_slices) * MI_SEGMENT_SLICE_SIZE;
@@ -865,6 +868,9 @@ static mi_segment_t* mi_segment_alloc(size_t required, size_t page_alignment, mi
   size_t pre_size;
   size_t segment_slices = mi_segment_calculate_slices(required, &pre_size, &info_slices);
 
+  // mi_page_t.slice_count type is uint32_t
+  if (segment_slices > (size_t)UINT32_MAX) return NULL;
+
   // Commit eagerly only if not the first N lazy segments (to reduce impact of many threads that allocate just a little)
   const bool eager_delay = (// !_mi_os_has_overcommit() &&             // never delay on overcommit systems
                             _mi_current_thread_count() > 1 &&       // do not delay for the first N threads