backport the following seven patches
malloc: Add madvise support for Transparent Huge Pages
malloc: Add THP/madvise support for sbrk
malloc: Move mmap logic to its own function
malloc: Add Huge Page support for mmap
malloc: Add Huge Page support to arenas
malloc: Move MORECORE fallback mmap to sysmalloc_mmap_fallback
malloc: Enable huge page support on main arena
Signed-off-by: Yang Yanchao <yangyanchao6@huawei.com>
