Restore unnamed_addr on vtables in -fno-rtti builds (#201846)
This is a follow-up to #200108 which dropped unnamed_addr from vtables
since it can break dynamic_cast under some circumstances. However, that
caused significant binary size regressions due to preventing ICF of
vtables.
This patch restores unnamed_addr on vtables in -fno-rtti builds, since
those do not support dynamic_cast, recovering the binary size savings at
least for those using that configuration.