[C++11] Introduce ObjectFile::sections().

Summary:
This adds ObjectFile::section_iterator_range, that allows to write
range-based for-loops running over all sections of a given file.
Several files from lib/ are converted to the new interface. Similar fixes
should be applied to a variety of llvm-* tools.

Reviewers: rafael

Reviewed By: rafael

CC: llvm-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D3069

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203799 91177308-0d34-0410-b5e6-96231b3b80d8