[analyzer] Add pointer escape type param to checkPointerEscape callback

[analyzer] Add pointer escape type param to checkPointerEscape callback

The checkPointerEscape callback previously did not specify how a
pointer escaped. This change includes an enum which describes the
different ways a pointer may escape. This enum is passed to the
checkPointerEscape callback when a pointer escapes. If the escape
is due to a function call, the call is passed. This changes
previous behavior where the call is passed as NULL if the escape
was due to indirectly invalidating the region the pointer referenced.

A patch by Branden Archer!

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174677 91177308-0d34-0410-b5e6-96231b3b80d8