Poking around the web suggests that the kernels can be pre-treated to remove the cyanide precursors; alternately, the liqueur might just be artificially flavored; the main component of the bitter-almond taste, benzaldehyde, is cheap and nontoxic. In the US, if you buy bitter almond flavoring for cooking, it’s likely mostly benzaldehyde; real bitter almond oil is highly regulated in the US because of the toxicity.