[analyzer] Look through temporary destructors when finding a region to construct.

Fixes a false positive when temporary destructors are enabled where a temporary
is destroyed after a variable is constructed but before the VarDecl itself is
processed, which occurs when the variable is in the condition of an if or while.

Patch by Alex McCarthy, with an extra test from me.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@205661 91177308-0d34-0410-b5e6-96231b3b80d8