Implement a correct copy constructor for Record. Now that we're using the ID number...

Implement a correct copy constructor for Record.  Now that we're using the ID number as a key in maps (for determinism), it is imperative that ID numbers be globally unique, even when we copy construct a Record.
This fixes some obscure failure cases involving registers defined inside multiclasses or foreach constructs that would not receive a unique ID, and would end up being omitted from the AsmMatcher tables.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164251 91177308-0d34-0410-b5e6-96231b3b80d8