Bug #156593. Use pkgconfig for libidl-2, not libIDL-config-2. r=cls

configure.in

@@ -4205,7 +4205,7 @@ MOZ_ARG_WITHOUT_BOOL(libIDL,
 if test "$SKIP_IDL_CHECK" = "no"
 then
     if test "$MOZ_ENABLE_GTK2"; then
-        AM_PATH_LIBIDL_2($LIBIDL_VERSION,,_LIBIDL_NOT_FOUND=1)
+        PKG_CHECK_MODULES(LIBIDL, libIDL-2.0 >= 0.8.0,,_LIBIDL_NOT_FOUND=1)
     else
         AM_PATH_LIBIDL($LIBIDL_VERSION,,_LIBIDL_NOT_FOUND=1)
     fi