[compiler-rt] Add support for the dynamic shadow allocation

[compiler-rt] Add support for the dynamic shadow allocation

Summary:
This patch is adding support for dynamic shadow allocation.

This is a merge and re-commit of the following patches.

```
[compiler-rt] Fix Asan build on Android
  https://reviews.llvm.org/D24768
[compiler-rt] Add support for the dynamic shadow allocation
  https://reviews.llvm.org/D23363
```

This patch needed to re-land at the same time:
```
[asan] Support dynamic shadow address instrumentation
  https://reviews.llvm.org/D23354
```

Reviewers: rnk, zaks.anna

Subscribers: tberghammer, danalbert, kubabrecka, dberris, chrisha, llvm-commits

Differential Revision: https://reviews.llvm.org/D25104

llvm-svn: 282882