Add C++ global operator {new,new[],delete,delete[]}(unsigned {int,long}) to the

memory builtins as equivalent to malloc/free.

This is different from any attribute we have. For example, you can delete the
allocators when their result is unused, but you can't collapse two calls to the
same function, even if no global/memory state has changed in between. The
noalias return states that the result does not alias any other pointer, but
instcombine optimizes malloc() as though the result is non-null for the purpose
of eliminating unused pointers.

llvm-svn: 127673