slow V3 configures (was Re: ICE during bootstrap.)

[Akim Demaille]

| If it's really a problem, we can also cache groups of test in one
| cache, like
|   is-math-stuff-cached
|     eval cached-setting-of-all-math-stuff
|   else
|     foreach math-test a
|       test-for-cached-answer-a-oh-it's-there-never-mind
|       else
|         ...
|       end
|       update-cached-setting-of-all-math-stuff
|     endfor
|   end

The Autoconf way to do this is to have a big macro which includes all
the tests you depend upon, and just AC_REQUIRE this macro.

AC_DEFUN([MY_MATH_TESTS],
[foreach math-test a
  test-for-cached-answer-a-oh-it's-there-never-mind
  else
    ...
  end
  update-cached-setting-of-all-math-stuff
endfor])

AC_REQUIRE([MY_MATH_TESTS])