Added Irix to the list of operating systems that can use -Wl,-rpath.

configure

@@ -3577,7 +3577,7 @@ if eval "test \"`echo '$''{'LINKER_RPATH'+set}'`\" = set"; then
 else
   LINKER_RPATH=
     case "$host_os" in
-    linux* | freebsd* | netbsd* | openbsd*)
+    linux* | freebsd* | netbsd* | openbsd* | irix*)
       # I believe this only works with GNU ld [pere 2001-04-16]
       LINKER_RPATH="-Wl,-rpath,"
       ;;