FreeBSD doesn't require the dl{open,close,sym,error} functions, as they are

scrappy · scrappy · commit 4f8db3eb4c61 · 1997-01-03T04:59:01.000Z
already included in the system libraries.

Used if !defined(__FreeBSD__) to single FreeBSD out from the other BSD44
derived OSs
diff --git a/src/backend/port/BSD44_derived/dl.c b/src/backend/port/BSD44_derived/dl.c
@@ -45,6 +45,8 @@ static char sccsid[] = "@(#)dl.c	5.4 (Berkeley) 2/23/91";
 
 #include "port-protos.h"
 
+#if !defined(__FreeBSD__) 
+
 static char	error_message[BUFSIZ];
 
 char *
@@ -101,3 +103,5 @@ BSD44_derived_dlclose(void *handle)
 	dlclose(handle);
 #endif
 }
+
+#endif /* __FreeBSD__ */
diff --git a/src/backend/port/BSD44_derived/port-protos.h b/src/backend/port/BSD44_derived/port-protos.h
@@ -6,7 +6,7 @@
  *
  * Copyright (c) 1994, Regents of the University of California
  *
- * $Id: port-protos.h,v 1.3 1996/10/31 11:09:37 scrappy Exp $
+ * $Id: port-protos.h,v 1.4 1997/01/03 04:59:01 scrappy Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -35,10 +35,17 @@
  * begin with an underscore is fairly tricky, and some versions of
  * NetBSD (like 1.0, and 1.0A pre June 1995) have no dlerror.)
  */
-#define	pg_dlopen(f)	BSD44_derived_dlopen(f, 1)
-#define	pg_dlsym	BSD44_derived_dlsym
-#define	pg_dlclose	BSD44_derived_dlclose
-#define	pg_dlerror	BSD44_derived_dlerror
+#if !defined(__FreeBSD__)
+# define	pg_dlopen(f)	BSD44_derived_dlopen(f, 1)
+# define	pg_dlsym	BSD44_derived_dlsym
+# define	pg_dlclose	BSD44_derived_dlclose
+# define	pg_dlerror	BSD44_derived_dlerror
+#else
+# define	pg_dlopen(f)	dlopen(f, 1)
+# define	pg_dlsym	dlsym
+# define	pg_dlclose	dlclose
+# define	pg_dlerror	dlerror
+#endif
 
 char *		BSD44_derived_dlerror(void);
 void *		BSD44_derived_dlopen(const char *filename, int num);
