[scudo][standalone] Minor corrections

Summary:
Few corrections with no functional change:
- replacing `%zd` with `%zu` all around: the values are unsigned
- prefer `MAP_ANONYMOUS` to `MAP_ANON` (it's deprecated)
- remove the unused `enum LinkerInitialized`
- mark a parameter as `UNUSED` in Fuchsia's `getRandom`
- correct the casing of a variable and use `nullptr` instead of 0 for
  pointers in `list.h`
- reorder some `typedef` to be consistent between `signed` and
  `unsigned`

Reviewers: eugenis, vitalybuka, morehouse, hctim

Reviewed By: vitalybuka, morehouse

Subscribers: delcypher, #sanitizers, llvm-commits

Tags: #llvm, #sanitizers

Differential Revision: https://reviews.llvm.org/D65660

llvm-svn: 368585