[llvm] [llvm-exegesis] Use hex values when parsing memory mappings (PR #72620)

[Clement Courbet via llvm-commits]

legrosbuffle wrote:

As this change is not backwards compatible we might be breaking people with no way for them/us to know. I see two options:

 - Support both decimal and hexadecimal. Prefix the latter with `0x`
 - Add a new deirective ` LLVM-EXEGESIS-MEM-MAP-HEX`  that reads hex values.

https://github.com/llvm/llvm-project/pull/72620