* Checks that the SDK specified with --enable-universalsk=VALUE exists.

* Fall back to the default system SDK when specifying --enable-universalsk
  without a value and the 10.4u SDK is not avaiable.

Port of fix for issue 4834 from the trunk.
diff --git a/configure.in b/configure.in
index 4459ec3..58ceea6 100644
--- a/configure.in
+++ b/configure.in
@@ -86,12 +86,17 @@
 AC_SUBST(CONFIG_ARGS)
 CONFIG_ARGS="$ac_configure_args"
 
+AC_MSG_CHECKING([for --enable-universalsdk])
 AC_ARG_ENABLE(universalsdk,
 	AC_HELP_STRING(--enable-universalsdk@<:@=SDKDIR@:>@, Build against Mac OS X 10.4u SDK (ppc/i386)),
 [
 	case $enableval in
 	yes)
 		enableval=/Developer/SDKs/MacOSX10.4u.sdk
+		if test ! -d "${enableval}"
+		then
+			enableval=/
+		fi
 		;;
 	esac
 	case $enableval in
@@ -101,12 +106,23 @@
 		;;
 	*)
 		UNIVERSALSDK=$enableval
+		if test ! -d "${UNIVERSALSDK}"
+		then
+			AC_MSG_ERROR([--enable-universalsdk specifies non-existing SDK: ${UNIVERSALSDK}])
+		fi
 		;;
 	esac
+	
 ],[
    	UNIVERSALSDK=
 	enable_universalsdk=
 ])
+if test -n "${UNIVERSALSDK}"
+then
+	AC_MSG_RESULT(${UNIVERSALSDK})
+else
+	AC_MSG_RESULT(no)
+fi
 AC_SUBST(UNIVERSALSDK)
 
 AC_SUBST(ARCH_RUN_32BIT)