Include gvcjob.h in gvcint.h

gvcint.h uses gvtextlayout_engine_t which is declared in gvcjob.h.

This means that in order to use gvcint.h, one must include gvcjob.h. This is particularly problematic because gvcint.h comes before gvcjob.h, alphabetically, which leads to a broken build after running an autoformatter.