[llvm] [TableGen, CodeGen, CHERI] Add support for the cPTR wildcard value type. (PR #158426)

[Kelvin Li via llvm-commits]

kkwli wrote:

@resistor The test `llvm/test/TableGen/CPtrWildcard.td` fails on `powerpc64le-*-linux` and `powerpc64-ibm-aix`. It generates:
```
"/* 8*/ OPC_CheckChild1Type, /*MVT::c64*/1|128,2/*257*/," instead of
"/* 8*/ OPC_CheckChild1Type, /*MVT::c64*/126|128,1/*254*/,"

"/*    18*/ OPC_CheckChild1Type, /*MVT::c128*/2|128,2/*258*/," instead of
"/*    18*/ OPC_CheckChild1Type, /*MVT::c128*/127|128,1/*255*/,"
```
Should those numbers be different on different platforms? Or is there something that can be tolerable?

https://github.com/llvm/llvm-project/pull/158426