Move build procedure to main source

[blakemcbride]

Right now, the (not terribly standard) build procedure is located on a website rather than part of the source distribution. Here is an almost guaranteed sequence of events:

1. People download and archive a copy of the source code.
2. Over time (years), swipl stops getting maintained, loses popularity, and the website hosting the build procedure disappears.
3. Some people who have archived copies of swipl want to build the system but can't find any build instructions.
4. Swipl essentially disappears because, although there is interest, there's not enough interest to rediscover the build process.

Thus, separating the source from the build procedure assures an earlier demise of the system.

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Having the build procedure on a website is all well and good. However, I think it is critical that a copy be maintained in the main source for the system.

[JanWielemaker]

Thanks for the suggestion. Seems minor to me. The build procedure is pretty much standard: cmake, working with Unix make, ninja or Microsoft nmake (and probably more; not tested) backends. The main issue is getting the dependencies. That is a highly platform dependent issue for which I think the website is more flexible than the main source.

Note that the build procedure is automated in several of the files under scripts (including dependencies for e.g. MacOS), Dockerfiles and build specifications for many operating systems.