Reviewed-by: shade, stuefe, coleenp

Summary: Made EMPTY_STACK non-const, so it will not be placed in read-only BSS section.
Reviewed-by: stuefe, martin
Contributed-by: zhaixiang@loongson.cn

Summary: Refactored emptyStack to a static member of NativeCallStack, which is accessible in minimal build.
Reviewed-by: coleenp, dholmes

Summary: Dynamic allocate _reserved_regions instead of static object to avoid racing during process exit
Reviewed-by: dholmes, coleenp

Summary: Enhance scalability of native memory tracking
Reviewed-by: coleenp, ctornqvi, gtriantafill

Summary: Disallow increasing native memory tracking level
Reviewed-by: hseigel, ctornqvi, gtriantafill