Add some AS_CASE logic to configure.ac, fixes bug #551376.

Add AC_USE_SYSTEM_EXTENSIONS macro, fixes bug #127000.

Drop AM_MAINTAINER_MODE macro, upstream no longer uses this
for xorg modules.

--- xconsole-1.0.6/configure.ac
+++ xconsole-1.0.6/configure.ac
@@ -29,10 +29,10 @@
 	[xconsole])
 AC_CONFIG_SRCDIR([Makefile.am])
 AC_CONFIG_HEADERS([config.h])
+AC_USE_SYSTEM_EXTENSIONS
 
 # Initialize Automake
 AM_INIT_AUTOMAKE([foreign dist-bzip2])
-AM_MAINTAINER_MODE
 
 # Require X.Org macros 1.8 or later for MAN_SUBSTS set by XORG_MANPAGE_SECTIONS
 m4_ifndef([XORG_MACROS_VERSION],
@@ -53,12 +53,17 @@
 
 AC_SEARCH_LIBS(openpty, [util])
 AC_CHECK_FUNC(openpty, [HAS_OPENPTY="yes"])
-if test "x$HAS_OPENPTY" = "xyes" ; then
+AS_IF([test "x$HAS_OPENPTY" = "xyes"], [
 	AC_DEFINE([HAS_OPENPTY], 1,
 		[Define to 1 if you have the 'openpty' function.])
-	AC_CHECK_HEADERS([util.h libutil.h pty.h], [break])
-fi
-
+	AC_CANONICAL_BUILD
+	AS_CASE([$build_os],
+	  [darwin* | netbsd* | openbsd*], [AC_CHECK_HEADER([util.h], [AC_DEFINE([HAVE_UTIL_H], 1)])],
+	  [freebsd*], [AC_CHECK_HEADER([libutil.h], [AC_DEFINE([HAVE_LIBUTIL_H], 1)])],
+	  [*linux-gnu], [AC_CHECK_HEADER([pty.h], [AC_DEFINE([HAVE_PTY_H], 1)])],
+	  [AC_CHECK_HEADERS([util.h libutil.h pty.h], [break])]
+	)
+],[])
 
 AC_CONFIG_FILES([
 	Makefile