[clang] [llvm] [RISC-V]Implement -m{,no}fence-tso (PR #151638)

[Philip Reames via llvm-commits]

preames wrote:

The recommendation is the issue you linked appears to be to upgrade to a newer OpenSBI version.  Why should we add a toolchain option for this at all?  Is this being discussed on the gcc side?  Is there a concern about performance?  If so, is there any report/data to substantiate that concern?   

https://github.com/llvm/llvm-project/pull/151638