iterator_range for machine block terminators.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206421 91177308-0d34-0410-b5e6-96231b3b80d8
[c++11] Tidy up AsmPrinter.cpp.

Range'ify loops and tidy up some by-reference handling. No functional
change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206422 91177308-0d34-0410-b5e6-96231b3b80d8