Call the correct @llvm.objectsize.

The following code would crash clang:

void foo(unsigned *const __attribute__((pass_object_size(0))));
void bar(unsigned *i) { foo(i); }

This is because we were always selecting the version of
`@llvm.objectsize` that takes an i8* in CodeGen. Passing an i32* as an
i8* makes LLVM very unhappy.

(Yes, I'm surprised that this remained uncaught for so long, too. :) )

As an added bonus, we'll now also use the appropriate address space when
emitting @llvm.objectsize calls.

llvm-svn: 295805