[clang] [compiler-rt] [rtsan][clang] Add Hexagon support for RTSan (PR #200313)

[Chris Apple via cfe-commits]

cjappl wrote:

This all seems straightforward enough to me. 

Will you talk to me about the support/test plan? For machines/OSs/archs that us codeowners don't have, I just want to make sure there is intention of support if there are any test failures or bugs that appear.

Also pinging @davidtrevelyan for a review

https://github.com/llvm/llvm-project/pull/200313