[asan] Support dynamic shadow address instrumentation

Summary:
This patch is adding the support for a shadow memory with
dynamically allocated address range.

The compiler-rt needs to export a symbol containing the shadow
memory range.

This is required to support ASAN on windows 64-bits.

Reviewers: kcc, rnk, vitalybuka

Subscribers: zaks.anna, kubabrecka, dberris, llvm-commits, chrisha

Differential Revision: https://reviews.llvm.org/D23354

llvm-svn: 282881