What is going on grammatically in the opening line of One Hundred Years of Solitude?

The verb be followed by a to-infinitive is used in historical narratives to convey that something took place later than the narrative moment. In your example,

Many years later, as he faced the firing squad, Colonel Aureliano Buendía was to remember that distant afternoon when his father took him to discover ice.

the translator uses this construction to establish two historical times: the narrative moment “when his father took him to discover ice” and a later time “when [he] was to remember”. It is important that he establishes the narrative moment, because proper understanding of the next clause

At that time Macondo was a village of twenty adobe houses

requires the reader to know that the narrative moment has already been established, meaning the text is describing the Macondo of Buendía’s childhood, not of his later life.

Other examples:

Here he was to remain until he died. (Earnest Brehaut, “Introduction” from his translation of Gregory of Tours’ History of the Franks) [he remained there after the narrative moment, when he was shut in to a cell]

This was to be an eventful day for the travelers. (L. Frank Baum, The Wonderful Wizard of Oz) [the referenced events occurred after the narrative moment, when the day began]

For the rest of his career, he was to brood on those events. (Brittanica, “English Literature: The Romantic Period”) [Wordsworth brooded after the narrative moment, when Britain declared war]

Only individual words have tense, not multiword phrases like was to remember.

Thus the tense of was is the past tense. The construction be to INFINITIVE is a periphrastic expression in English with a particular meaning. In its epistemic mode, it conveys the inevitable future or near present or near future, but not quite so near as be about to does. (In its deontic mode, not used here, it’s a light command.) The Spanish did the same. The OED says of be plus an infinitive that it means:

With infinitive. Expressing an appointed or arranged future action; (hence also) expressing necessity, obligation, duty, fitness, or appropriateness.

So this acts effectively like a modal, and indeed has both an epistemic mode and a deontic mode. Here the epistemic mode is used, the one corresponding to simple will rather than to must.

To understand what the author was really trying to convey requires looking at the original, not the translation.

Muchos años después, frente al pelotón de fusilamiento, el coronel Aureliano Buendía había de recordar aquella tarde remota en que su padre lo llevó a conocer el hielo.

The tense used in the Spanish verb corresponding to the English was was the “pretérito imperfecto de indicativo” (había rather than hubo), a simple tense often just called the “imperfect” in English.

On the other hand, the tense used for the Spanish verb corresponding to the English translation’s took was the “pretérito” (llevó not llevaba), usually called the preterite or simple past indicative in English.

The problem is that unlike Spanish, English does not offer a pair of contrasting morphological (inflectional) past tenses where one past tense has the imperfect aspect and the other past tense has the perfect aspect.

That means there is no easy and direct way to express that distinction in English. You cannot tell just by looking at their inflectional morphology that that was had originally been an ongoing / narrative / imperfect tense in Spanish but that that took had originally been a completed / perfect / preterite in Spanish.

Another way which the original’s había de recordar could have been translated into English is would remember rather than was to remember. Here would serves as the past tense of the modal verb will to express the was going to type of aspect.

English assembles chained-together sequences of verbs in various inflections to express many nuanced and complex combinations of tense, mode, and aspect. There is almost no end of these, and there’s no reason that each should carry some special name.

He would have been going to be hanged by then, assuming the jury came back the way we expected it to.

There’s no special “name” for that particular periphrastic construction, any more than there is a “name” for the periphrastic expression was to remember in English. But don’t feel bad: había de recordar has no name for that construction in Spanish, either. It’s just something you do. It has no name nor needs one.

Same goes for took to discover in English, or llevó a conocer in Spanish. Those things don’t have their own names; they’re just periphrastic verbs in the past tense.