Don't use alias from derived dtor to base dtor at -O0.

This patch disables aliasing (and rauw) of derived dtors to base dtors at -O0.
This optimization can have a negative impact on the debug quality.

This was a latent bug for some time with local classes, but got noticed when it
was generalized and broke gdb's destrprint.exp.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@194618 91177308-0d34-0410-b5e6-96231b3b80d8