Isolation: Fix the enablement of PR_SET_NO_NEW_PRIVS.

This prctl(2) option is checked for in auto/isolation, unfortunately due
to a typo this feature has never been enabled.

In the auto/isolation script the feature name was down as
NXT_HAVE_PR_SET_NO_NEW_PRIVS0, which means we end up with the following
in build/nxt_auto_config.h

  #ifndef NXT_HAVE_PR_SET_NO_NEW_PRIVS0
  #define NXT_HAVE_PR_SET_NO_NEW_PRIVS0  1
  #endif

Whereas everywhere else is checking for NXT_HAVE_PR_SET_NO_NEW_PRIVS.

This also guards the inclusion of sys/prctl.h in src/nxt_process.c which
is required by a subsequent commit.

Fixes: e2b53e1 ("Added "rootfs" feature.")
Reviewed-by: Alejandro Colomar <[email protected]>
Signed-off-by: Andrew Clayton <[email protected]>

Author: ac000

auto/isolation

@@ -90,7 +90,7 @@ nxt_feature_test="#include <mntent.h>
 
 
 nxt_feature="prctl(PR_SET_NO_NEW_PRIVS)"
-nxt_feature_name=NXT_HAVE_PR_SET_NO_NEW_PRIVS0
+nxt_feature_name=NXT_HAVE_PR_SET_NO_NEW_PRIVS
 nxt_feature_run=no
 nxt_feature_incs=
 nxt_feature_libs=