General host configuration fragment purge

[DJ Delorie]

> Plain make is technically not supported at all unless ...

Of course plain make is supported.  That's pretty much what the first
stage of a bootstrap is.  It may be that the user needs to manually do
a "stage1" with special options, *install* it somewhere, and do a
bootstrap in a separate build directory, if the bundled compiler and
gcc differ significantly in what autoconf will detect about them.

If what you mean is "plain make is not guaranteed to automagically
select the right bundled compiler/options/tools" then I'd agree.  But
IMHO any configure magic that the platform maintainer wishes to add to
make it easier for their platform to "just work" is a Good Thing, as
long as its complexity is localized.