selftests/ptrace: add test cases for dead-locks

This adds test cases for ptrace deadlocks.

Additionally fixes a compile problem in get_syscall_info.c,
observed with gcc-4.8.4:

get_syscall_info.c: In function 'get_syscall_info':
get_syscall_info.c:93:3: error: 'for' loop initial declarations are only
allowed in C99 mode
for (unsigned int i = 0; i < ARRAY_SIZE(args); ++i) {
^
get_syscall_info.c:93:3: note: use option -std=c99 or -std=gnu99 to compile
your code

Signed-off-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>