[Sanitizer] Using huge page on FreeBSD for shadow mapping

- Unless explicit configuration, using FreeBSD super pages feature for shadow mapping.
- asan only for now.

Reviewers: dim, emaste, vitalybuka

Reviewed By: vitalybuka

Differential Revision: https://reviews.llvm.org/D65851

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@370008 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed