[builtins] Implement emulated TLS on Windows.

Summary:
LLVM JIT needs to be able to use emulated TLS on all platforms, and this provides a reference one can compile to enable emutls for Linux/Mac/Windows.

Reviewers: chh, howard.hinnant

Reviewed By: chh

Subscribers: mgorny, llvm-commits

Differential Revision: https://reviews.llvm.org/D30787

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@301350 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed