This process was sometimes called linkage editing and the output known as a load module. A compiler works with what are sometimes called 3GL and higher-level languages. An assembler works on programs written using a processor's assembler language.
In general, however, when between vowels (as in exactamente) the Spanish x is pronounced like the English ks sound but softer or less explosive. When it comes before another consonant (as in expediciÃ³n), it has the s sound in some regions/countries but the soft ks sound in others.
No, there's no regional variation, it's the pronunciation that varies. Unfortunately I don't think a rule exists, what I have noticed is this, though: x at the beginning of words is always like sh: xarope, xampu, xÃ­cara. x before a consonant is always like an s: exterior, externo, expressar.