Emit remember_state CFI in the same code region as restore_state.

Summary:
While creating remember_state/restore_state CFI sequences, we
were always placing remember_state instruction into the first
basic block. However, when we have hot-cold splitting, the cold
part has and independent FDE entry in .eh_frame, and thus the
restore_state instruction was missing its counter part.

The fix is to adjust the basic block that is used for placing
remember_state instruction whenever we see the hot-cold split
boundary.

(cherry picked from FBD3767102)