Add target property for whether thread-local storage is supported.  
Let me know if I messed up for some target.  Note that for Windows, we 
should be able to support it (MSVC supports "__declspec(thread)"), but 
I'm pretty sure LLVM doesn't know how to generate the correct code.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@69552 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed