Change macOS mmap tag to fix conflict with IOAccelerator

Tag 100 is assigned to "IOAccelerator" (the GPU driver stack on Apple silicon), which makes for confusing output when debugging.

To avoid conflicts, use a tag in the reserved application-specific range from 240–255 (inclusive).

All assigned tags: 94d3b45284/osfmk/mach/vm_statistics.h (L773-L775)

src/prim/unix/prim.c

@@ -240,7 +240,7 @@ static int unix_mmap_fd(void) {
   #if defined(VM_MAKE_TAG)
   // macOS: tracking anonymous page with a specific ID. (All up to 98 are taken officially but LLVM sanitizers had taken 99)
   int os_tag = (int)mi_option_get(mi_option_os_tag);
-  if (os_tag < 100 || os_tag > 255) { os_tag = 100; }
+  if (os_tag < 100 || os_tag > 255) { os_tag = 254; }
   return VM_MAKE_TAG(os_tag);
   #else
   return -1;