[compiler-rt] Add support for interception redirect exports.

Summary:
On windows, an export can be redirected to an other DLL.
This patch is adding the required support to the internal
GetProcAddress implementation.

This case was encountered by instrumenting chromium (win 64-bits)
using this GN configuration:
```
is_component_build = true
is_debug = false
enable_nacl = false
is_clang = true
is_asan = true
clang_base_path = "d:\src\llvm\ninja64"
clang_use_chrome_plugins = false
clang_version = "4.0.0"
```

The operating system is win7 (x64).
Visual Studio: 2015 Professional



Reviewers: rnk

Subscribers: llvm-commits, chrisha

Differential Revision: https://reviews.llvm.org/D22880

llvm-svn: 277294