[mimalloc] Remove no-longer-needed limit on emmalloc alignment (#21905)

#20704 removed the maximum alignment limit from emmalloc, so we no longer
need it in the mimalloc port. Without it, we can properly use the 4GB-aligned pages
that mimalloc requests.

Author: kripken

system/lib/mimalloc/src/prim/emscripten/prim.c

@@ -1,5 +1,5 @@
 /* ----------------------------------------------------------------------------
-Copyright (c) 2018-2023, Microsoft Research, Daan Leijen
+Copyright (c) 2018-2023, Microsoft Research, Daan Leijen, Alon Zakai
 This is free software; you can redistribute it and/or modify it under the
 terms of the MIT license. A copy of the license can be found in the file
 "LICENSE" at the root of this distribution.
@@ -78,17 +78,10 @@ int _mi_prim_alloc(size_t size, size_t try_alignment, bool commit, bool allow_la
   //       That assumes no one else uses sbrk but us (they could go up,
   //       scribble, and then down), but we could assert on that perhaps.
   *is_zero = false;
-  // emmalloc has some limitations on alignment size.
-  // TODO: Why does mimalloc ask for an align of 4MB? that ends up allocating
-  //       8, which wastes quite a lot for us in wasm. If that is unavoidable,
-  //       we may want to improve emmalloc to support such alignment. See also
-  //       https://github.com/emscripten-core/emscripten/issues/20645
+  // emmalloc has a minimum alignment size.
   #define MIN_EMMALLOC_ALIGN           8
-  #define MAX_EMMALLOC_ALIGN (1024*1024)
   if (try_alignment < MIN_EMMALLOC_ALIGN) {
     try_alignment = MIN_EMMALLOC_ALIGN;
-  } else if (try_alignment > MAX_EMMALLOC_ALIGN) {
-    try_alignment = MAX_EMMALLOC_ALIGN;
   }
   void* p = emmalloc_memalign(try_alignment, size);
   *addr = p;
@@ -249,4 +242,3 @@ void _mi_prim_thread_associate_default_heap(mi_heap_t* heap) {
 
 }
 #endif
-