Move DroppedVariableStats to CodeGen lib (#120650)

To get Dropped variable statistics for MIR, we need to move the base
class DroppedVariableStats code to the CodeGen library because we cannot
have CodeGen link against Passes.

Also moved the code for the virtual functions to the header because
clang/lib/CodeGen doesn't link against llvm/lib/CodeGen however it does
link against Passes which contains the `class StandardInstrumentations`
code but not the definition for the virtual functions leading to the
error about not finding vtable for `class DroppedVariableStatsIR`

0 files changed, 0 insertions, 0 deletions