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 and other bug caused in chrome.
After this patch got reverted because of ScalarEvolution bug (D12719)
Merged after John McCall big patch (Added Address).

http://reviews.llvm.org/D11859
http://reviews.llvm.org/D12865