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

[Joe Nash via llvm-commits]

================
@@ -65,6 +65,8 @@
     flags=(re.M | re.S),
 )
 
+META_PTR_RE = re.compile(r"\<0x[a-f0-9]+\>", re.IGNORECASE)
----------------
Sisyph wrote:

```suggestion
MD_PTR_RE = re.compile(r"\<0x[a-f0-9]+\>", re.IGNORECASE)
```

MD is the typical abbreviation for Metadata. Or you could write out METADATA

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