[libFuzzer] Clean up headers and file formatting of LibFuzzer files.

Reorganize #includes to follow LLVM Coding Standards.
Include some missing headers. Required to use `Printf()`.

Aside from that, this patch contains no functional change.
It is purely a re-organization.

Differential Revision: https://reviews.llvm.org/D27363

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@289560 91177308-0d34-0410-b5e6-96231b3b80d8
23 files changed