[llvm] Add metadata pointer regex substitution to MIR update script (PR #163253)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> LLC prints metadata operands as pointers in MIR, meaning tests can fail due to stale values with future changes.

Can you work on fixing that rather than introducing a new script to workaround a bug 

https://github.com/llvm/llvm-project/pull/163253