autoconf: Changed Macro Writing

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1 18.5.5 Changed Macro Writing
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1 When defining your own macros, you should now use `AC_DEFUN' instead of
1 `define'.  `AC_DEFUN' automatically calls `AC_PROVIDE' and ensures that
1 macros called via `AC_REQUIRE' do not interrupt other macros, to
1 prevent nested `checking...' messages on the screen.  There's no actual
1 harm in continuing to use the older way, but it's less convenient and
1 attractive.  ⇒Macro Definitions.
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1    You probably looked at the macros that came with Autoconf as a guide
1 for how to do things.  It would be a good idea to take a look at the new
1 versions of them, as the style is somewhat improved and they take
1 advantage of some new features.
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1    If you were doing tricky things with undocumented Autoconf internals
1 (macros, variables, diversions), check whether you need to change
1 anything to account for changes that have been made.  Perhaps you can
1 even use an officially supported technique in version 2 instead of
1 kludging.  Or perhaps not.
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1    To speed up your locally written feature tests, add caching to them.
1 See whether any of your tests are of general enough usefulness to
1 encapsulate them into macros that you can share.
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