[C++11] Introduce SectionRef::relocations() to use range-based loops

Reviewers: rafael

Reviewed By: rafael

CC: llvm-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D3077

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203927 91177308-0d34-0410-b5e6-96231b3b80d8