Bear in mind that steps 1, 3, 4, 6, and 7 are not related to slashpackage. nrclark has got step #2 wrong, as all that it yields is the current source package version number not a URL and there's no real parsing going on (except for the shell stripping the trailing newline); and xyr step #8 is xyr own invention and not actually in the build instructions as given.
That leaves step #5. What that does is both fairly obvious and documented in the instructions. It tries out a whole bunch of compilers, compiler options, and implementations in turn to see which results in the best code. Ironically, it is probably the sort of thing that autotools might be persuaded to do. But in practice no-one would, or it would be buried under reams of copied-and-pasted cargo cult tests for things that the actual source at hand cannot in fact do without in the first place.
This is of course a long-recognized fly in any let's-just-use-autotools ointment, discussed over many years. (-:
That leaves step #5. What that does is both fairly obvious and documented in the instructions. It tries out a whole bunch of compilers, compiler options, and implementations in turn to see which results in the best code. Ironically, it is probably the sort of thing that autotools might be persuaded to do. But in practice no-one would, or it would be buried under reams of copied-and-pasted cargo cult tests for things that the actual source at hand cannot in fact do without in the first place.
This is of course a long-recognized fly in any let's-just-use-autotools ointment, discussed over many years. (-:
* https://news.ycombinator.com/item?id=5276876
* https://queue.acm.org/detail.cfm?id=2349257
* http://freshmeat.sourceforge.net/articles/stop-the-autoconf-...
* https://news.ycombinator.com/item?id=1499738
* https://news.ycombinator.com/item?id=4407486