Cleanup configure.in. Specifically:

- Don't call both AC_CHECK_FUNCS and AC_REPLACE_FUNC for 'hypot', as the
latter already does everything the former does (because it's implemented as
a call to the former.)

- Don't call AC_CHECK_FUNC() without any 'action' clauses or with an action
clause that just defines HAVE_<function>. Instead, call AC_CHECK_FUNCS,
which defines 'HAVE_<function>' of itself, possibly with aditional 'action'
clauses.

No checks are removed by this patch, only moved around, and some duplicates
are removed.
diff --git a/config.h.in b/config.h.in
index 32d5e85..5db7bd7 100644
--- a/config.h.in
+++ b/config.h.in
@@ -109,9 +109,6 @@
 /* Define this if your time.h defines altzone */
 #undef HAVE_ALTZONE
 
-/* Define this if you have gethostbyname() */
-#undef HAVE_GETHOSTBYNAME
-
 /* Define this if you have some version of gethostbyname_r() */
 #undef HAVE_GETHOSTBYNAME_R
 
@@ -335,6 +332,9 @@
 /* Define if you have the getgroups function.  */
 #undef HAVE_GETGROUPS
 
+/* Define if you have the gethostbyname function.  */
+#undef HAVE_GETHOSTBYNAME
+
 /* Define if you have the getlogin function.  */
 #undef HAVE_GETLOGIN