Revert r160254 temporarily.

It turns out that ASan relied on the at-the-end block insertion order to
(purely by happenstance) disable some LLVM optimizations, which in turn
start firing when the ordering is made more "normal". These
optimizations in turn merge many of the instrumentation reporting calls
which breaks the return address based error reporting in ASan.

We're looking at several different options for fixing this.

llvm-svn: 160256