IR: Add a configuration point for MDNodeInfo::isEqual, NFC

This commit has no functionality change, but it adds a configuration
point for MDNodeInfo::isEqual to allow custom uniquing of subclasses of
MDNode, minimizing the diff of a follow-up.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@266542 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed