base/allocator: Remove malloc_stats and mallopt when OS_APPLE

macOS and iOS do not support malloc_stats and mallopt, plus we'll
hit the following error if we define them.

../../chrome/tools/build/mac/verify_order: unordered symbols in Chromium Framework.framework/Versions/87.0.4260.0/Chromium Framework:
_malloc_stats
_mallopt

So, this patch removes them when OS_APPLE.

Bug: 998048
Change-Id: I5820670ce7b77d19b4f80acded73b3703b8aa478
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2400584Reviewed-by: Benoit L <lizeb@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Yuki Shiino <yukishiino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#805819}

base/allocator/allocator_shim_default_dispatch_to_partition_alloc.cc

@@ -7,6 +7,7 @@
 #include "base/allocator/partition_allocator/partition_alloc.h"
 #include "base/bits.h"
 #include "base/no_destructor.h"
+#include "build/build_config.h"
 
 namespace {
 
@@ -149,12 +150,16 @@ constexpr AllocatorDispatch AllocatorDispatch::default_dispatch = {
 
 extern "C" {
 
+#if !defined(OS_APPLE)
+
 SHIM_ALWAYS_EXPORT void malloc_stats(void) __THROW {}
 
 SHIM_ALWAYS_EXPORT int mallopt(int cmd, int value) __THROW {
   return 0;
 }
 
+#endif  // !defined(OS_APPLE)
+
 #ifdef HAVE_STRUCT_MALLINFO
 SHIM_ALWAYS_EXPORT struct mallinfo mallinfo(void) __THROW {
   return {};