Generating assumption loads of vptr after ctor call (fixed)

Generating call assume(icmp %vtable, %global_vtable) after constructor
call for devirtualization purposes.

For more info go to:
http://lists.llvm.org/pipermail/cfe-dev/2015-July/044227.html

Edit:
Fixed version because of PR24479.

http://reviews.llvm.org/D11859

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@245264 91177308-0d34-0410-b5e6-96231b3b80d8