Range-for some stuff related to RegClasses, and comment cases where range-for isn't suitable.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223260 91177308-0d34-0410-b5e6-96231b3b80d8
Simplify ownership of RegClasses by using list<CodeGenRegisterClass> instead of vector<CodeGenRegisterClass*>

This complicates a few algorithms due to not having random access, but
not by a huge degree I don't think (open to debate/design
discussion/etc).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223261 91177308-0d34-0410-b5e6-96231b3b80d8
Simplify CodeGenRegBank::inferMatchingSuperRegClass & its caller by passing an iterator rather than index

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223262 91177308-0d34-0410-b5e6-96231b3b80d8
range-for some things

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223263 91177308-0d34-0410-b5e6-96231b3b80d8