Set _XOPEN_SOURCE to 600 so that fchmod() will (hopefully) work on FreeBSD.

FossilOrigin-Name: 61a10452399db28cd5ea4ba9d416b87a34c2eddb
diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index 5950f23..d735a14 100644
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -193,20 +193,12 @@
 
 /*
 ** We need to define _XOPEN_SOURCE as follows in order to enable
-** recursive mutexes on most Unix systems.  But Mac OS X is different.
-** The _XOPEN_SOURCE define causes problems for Mac OS X we are told,
-** so it is omitted there.  See ticket #2673.
-**
-** Later we learn that _XOPEN_SOURCE is poorly or incorrectly
-** implemented on some systems.  So we avoid defining it at all
-** if it is already defined or if it is unneeded because we are
-** not doing a threadsafe build.  Ticket #2681.
-**
-** See also ticket #2741.
+** recursive mutexes on most Unix systems and fchmod() on OpenBSD.
+** But _XOPEN_SOURCE define causes problems for Mac OS X, so omit
+** it.
 */
-#if !defined(_XOPEN_SOURCE) && !defined(__DARWIN__) \
- && !defined(__APPLE__) && SQLITE_THREADSAFE
-#  define _XOPEN_SOURCE 500  /* Needed to enable pthread recursive mutexes */
+#if !defined(_XOPEN_SOURCE) && !defined(__DARWIN__) && !defined(__APPLE__)
+#  define _XOPEN_SOURCE 600
 #endif
 
 /*