[analyzer; alternate arrows] use the terminator condition as the location for 'entering loop body'

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@181291 91177308-0d34-0410-b5e6-96231b3b80d8
[analyzer; alternate edges] simplify optimization rules to look at control-flow conditions to prune edges.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@181292 91177308-0d34-0410-b5e6-96231b3b80d8