[llvm] Reland: "[Exegesis] Add the ability to dry-run the measurement phase (#121991)" (PR #122775)

[Min-Yih Hsu via llvm-commits]

mshockwave wrote:

> This seems to break tests on macOS: http://45.33.8.238/macm1/98920/step_10.txt
> 
> Please take a look and revert for now if it takes a while to fix.

The root cause of this problem was, again, relatively subtle: The RISC-V snippet object was generated by a MC assembler separated from the LLJIT engine, which was configured using the host triple. Therefore the host -- macosx in these cases -- would expect symbols to be prefixed by underscore, while RISC-V doesn't use that convention in any way at this moment.

https://github.com/llvm/llvm-project/pull/122775