Add UNSUPPORTED check in elf/tst-pldd.

The testcase forks a child process and runs pldd with PID of
this child.  On systems where /proc/sys/kernel/yama/ptrace_scope
differs from zero, pldd will fail with
/usr/bin/pldd: cannot attach to process 3: Operation not permitted

This patch checks if ptrace_scope exists, is zero "classic ptrace permissions"
or one "restricted ptrace".  If ptrace_scope exists and has a higher
restriction, then the test is marked as UNSUPPORTED.

The case "restricted ptrace" is handled by rearranging the processes involved
during the test.  Now we have the following process tree:
-parent: do_test (performs output checks)
--subprocess 1: pldd_process (becomes pldd via execve)
---subprocess 2: target_process (ptraced via pldd)

ChangeLog:

	* elf/tst-pldd.c (do_test): Add UNSUPPORTED check.
	Rearrange subprocesses.
	(pldd_process): New function.
	* support/Makefile (libsupport-routines): Add support_ptrace.
	* support/xptrace.h: New file.
	* support/support_ptrace.c: Likewise.

1 files changed, 1 insertions, 0 deletions

diff --git a/support/Makefile b/support/Makefile
index be90043801..ca238ee8b4 100644
--- a/support/Makefile
+++ b/support/Makefile
@@ -56,6 +56,7 @@ libsupport-routines = \
   support_format_hostent \
   support_format_netent \
   support_isolate_in_subprocess \
+  support_ptrace \
   support_openpty \
   support_paths \
   support_quote_blob \