[NFC][clang] Fix static analyzer concerns about AUTO_CAUSES_COPY

Reported by Coverity:

AUTO_CAUSES_COPY
Unnecessary object copies can affect performance

1. Inside "ODRHash.cpp" file, in clang::ODRHash::AddCXXRecordDecl(clang::CXXRecordDecl const *): Using the auto keyword without an & causes the copy of an object of type CXXBaseSpecifier.

2. Inside "Tokens.cpp" file, in clang::syntax::TokenBuffer::dumpForTests[abi:cxx11](): Using the auto keyword without an & causes the copy of an object of type DenseMapPair.

3. Inside "TargetID.cpp" file, in clang::getCanonicalTargetID[abi:cxx11](llvm::StringRef, llvm::StringMap<bool, llvm::MallocAllocator> const &): Using the auto keyword without an & causes the copy of an object of type pair.

Reviewed By: tahonermann, aaron.ballman

Differential Revision: https://reviews.llvm.org/D148639