Use range-based for loops and const-correct a few things.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222908 91177308-0d34-0410-b5e6-96231b3b80d8
Use unique_ptr to fix some memory leaks in Tablegen AsmMatcherEmitter.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222909 91177308-0d34-0410-b5e6-96231b3b80d8
Add missing 'override' keyword.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222911 91177308-0d34-0410-b5e6-96231b3b80d8