Enable memory-mapped I/O on FreeBSD and DragonFly.

FossilOrigin-Name: 2cdd647951ff5dca53576bb8be6dd6310a557571
diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index 862b2f6..c520e8a 100644
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -754,7 +754,9 @@
 # if defined(__linux__) \
   || defined(_WIN32) \
   || (defined(__APPLE__) && defined(__MACH__)) \
-  || defined(__sun)
+  || defined(__sun) \
+  || defined(__FreeBSD__) \
+  || defined(__DragonFly__)
 #   define SQLITE_MAX_MMAP_SIZE 0x7fff0000  /* 2147418112 */
 # else
 #   define SQLITE_MAX_MMAP_SIZE 0