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.
1 And yes, it can in fact be used in the singular.  Ze, hir (Xena ate hir food because ze was hungry.) Ze is pronounced like âzeeâ can also be spelled zie or xe, and replaces she/he/they. Hir is pronounced like âhereâ and replaces her/hers/him/his/they/theirs.