Fix ORCA build, by adding #include required for syscache ids.

syscache.h was previously included from parse_oper.h, but I removed that
in commit 8d77fb99. Turns out that gpdbwrappers.c was relying on that
indirect include.

src/include/gpopt/utils/gpdbdefs.h

@@ -30,6 +30,7 @@ extern "C" {
 #include "parser/parsetree.h"
 #include "utils/inval.h"
 #include "utils/lsyscache.h"
+#include "utils/syscache.h"
 #include "utils/datum.h"
 #include "utils/array.h"
 #include "utils/builtins.h"