[analyzer] Fix leak false positives on stuff put in C++/ObjC initializer lists.

The analyzer now realizes that C++ std::initializer_list objects and
Objective-C boxed structure/array/dictionary expressions can potentially
maintain a reference to the objects that were put into them. This avoids
false memory leak posivites and a few other issues.

This is a conservative behavior; for now, we do not model what actually happens
to the objects after being passed into such initializer lists.

rdar://problem/32918288
Differential Revision: https://reviews.llvm.org/D35216

llvm-svn: 314975