MDEV-329: MariaDB 5.5 does not use fdatasync().

The --debug-no-sync incorrectly defaulted to ON, disabling sync calls
by default which can loose data or cause corruption. Also, the code
used fsync() instead of the sometimes more efficient fdatasync().

config.h.cmake

@@ -150,6 +150,7 @@
 #cmakedefine HAVE_FCNTL 1
 #cmakedefine HAVE_FCONVERT 1
 #cmakedefine HAVE_FDATASYNC 1
+#cmakedefine HAVE_DECL_FDATASYNC 1
 #cmakedefine HAVE_FESETROUND 1
 #cmakedefine HAVE_FINITE 1
 #cmakedefine HAVE_FP_EXCEPT 1

sql/mysqld.cc

@@ -6161,7 +6161,7 @@ struct my_option my_long_options[]=
 #endif
   {"debug-no-sync", 0,
    "Disables system sync calls. Only for running tests or debugging!",
-   &my_disable_sync, &my_disable_sync, 0, GET_BOOL, NO_ARG, 1, 0, 0, 0, 0, 0},
+   &my_disable_sync, &my_disable_sync, 0, GET_BOOL, NO_ARG, 0, 0, 0, 0, 0, 0},
 #ifdef HAVE_REPLICATION
   {"debug-sporadic-binlog-dump-fail", 0,
    "Option used by mysql-test for debugging and testing of replication.",