[Sanitizers] Add support for RISC-V 64-bit
This has been tested with gcc trunk on openSUSE Tumbleweed on the HiFive Unleashed.
Patch by Andreas Schwab (schwab)
Reviewed By: luismarques
Subscribers: mhorne, emaste, luismarques, asb, mgorny, fedor.sergeev, simoncook, kito-cheng, shiva0217, rogfer01, rkruppe, lenary, s.egerton, #sanitizers, llvm-commits
Tags: #llvm, #sanitizers
Differential Revision: https://reviews.llvm.org/D66870