Add new test traceme4 in t_ptrace

This test verifies calling raise(2) with the SIGCONT argument in the child.
The parent is notified with it and asserts that WIFCONTINUED() and
WIFSTOPPED() are both set.

XXX: This behavior is surprising. Linux for the same code-path returns false
for WIFCONTINUED() and true for WIFSTOPPED().

Include <stdlib.h> for EXIT_FAILURE.

This code covers (uncovers issues?) WIFCONTINUED() and is the last planned
test in the ptraceme category.

Sponsored by <The NetBSD Foundation>.

For future reference and convenience, an out-of-ATF test is as follows:
#include <sys/param.h>
#include <sys/types.h>
#include <sys/ptrace.h>
#include <sys/wait.h>
#include <assert.h>
#include <err.h>
#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

#define ATF_REQUIRE(a) assert(a)

#if defined(linux)
#define WALLSIG __WALL
#define sys_signame sys_siglist
#endif

int main(int argc, char **argv)
{
        int status;
        const int exitval = 5;
        const int sigval = SIGSTOP, sigsent = SIGCONT;
        pid_t child, wpid;

        printf("1: Before forking process PID=%d\n", getpid());
        ATF_REQUIRE((child = fork()) != -1);
        if (child == 0) {
                /* printf(3) messages from a child aren't intercepted by ATF */
                /* "2: Child process PID=%d\n", getpid() */

                /* "2: Before calling ptrace(PT_TRACE_ME, ...)\n" */
                if (ptrace(PT_TRACE_ME, 0, NULL, 0) == -1) {
                        /* XXX: Is it safe to use ATF functions in a child? */
                        err(EXIT_FAILURE, "2: ptrace(2) call failed with "
                            "status %s", sys_errlist[errno]);
                }

                /* "2: Before raising SIGSTOP\n" */
                raise(sigval);

                /* "2: Before raising SIGCONT\n" */
                raise(sigsent);

                /* "2: Before calling _exit(%d)\n", exitval */
                _exit(exitval);
        } else {
                printf("1: Parent process PID=%d, child's PID=%d\n", getpid(),
                    child);

                printf("1: Before calling waitpid() for the child\n");
                wpid = waitpid(child, &status, 0);

                printf("1: Validating child's PID (expected %d, got %d)\n",
                    child, wpid);
                ATF_REQUIRE(child == wpid);

                printf("1: Ensuring that the child has not been exited\n");
                ATF_REQUIRE(!WIFEXITED(status));

                printf("1: Ensuring that the child has not been continued\n");
                ATF_REQUIRE(!WIFCONTINUED(status));

                printf("1: Ensuring that the child has not been terminated "
                    "with a signal\n");
                ATF_REQUIRE(!WIFSIGNALED(status));

                printf("1: Ensuring that the child has been stopped\n");
                ATF_REQUIRE(WIFSTOPPED(status));
                printf("1: Verifying that he child has been stopped with the"
                    " %s signal (received %s)\n", sys_signame[sigval],
                    sys_signame[WSTOPSIG(status)]);
                ATF_REQUIRE(WSTOPSIG(status) == sigval);

                printf("1: Before resuming the child process where it left "
                    "off and without signal to be sent\n");
                ATF_REQUIRE(ptrace(PT_CONTINUE, child, (void *)1, 0)
                    != -1);

                printf("1: Before calling waitpid() for the child\n");
                wpid = waitpid(child, &status, WALLSIG);

                printf("1: Validating that child's PID is still there\n");
                ATF_REQUIRE(wpid == child);

                printf("1: Ensuring that the child has not been exited\n");
                ATF_REQUIRE(!WIFEXITED(status));

                printf("1: Ensuring that the child has been continued\n");
                ATF_REQUIRE(WIFCONTINUED(status));

                printf("1: Ensuring that the child has not been terminated "
                    "with a signal\n");
                ATF_REQUIRE(!WIFSIGNALED(status));

                printf("1: Ensuring that the child has not been stopped\n");
                ATF_REQUIRE(WIFSTOPPED(status));

                printf("1: Before resuming the child process where it left "
                    "off and without signal to be sent\n");
                ATF_REQUIRE(ptrace(PT_CONTINUE, child, (void *)1, 0) != -1);
                printf("1: Before calling waitpid() for the child\n");
                wpid = waitpid(child, &status, 0);

                printf("1: Validating that child's PID is still there\n");
                ATF_REQUIRE(wpid == child);

                printf("1: Ensuring that the child has been exited\n");
                ATF_REQUIRE(WIFEXITED(status));

                printf("1: Ensuring that the child has not been continued\n");
                ATF_REQUIRE(!WIFCONTINUED(status));

                printf("1: Ensuring that the child has not been terminated "
                    "with a signal\n");
                ATF_REQUIRE(!WIFSIGNALED(status));

                printf("1: Ensuring that the child has not been stopped\n");
                ATF_REQUIRE(!WIFSTOPPED(status));

                printf("1: Verifying that he child has exited with the "
                    "%d status (received %d)\n", exitval, WEXITSTATUS(status));
                ATF_REQUIRE(WEXITSTATUS(status) == exitval);

                printf("1: Before calling waitpid() for the exited child\n");
                wpid = waitpid(child, &status, 0);

                printf("1: Validating that child's PID no longer exists\n");
                ATF_REQUIRE(wpid == -1);

                printf("1: Validating that errno is set to %s (got %s)\n",
                    sys_errlist[ECHILD], sys_errlist[errno]);
                ATF_REQUIRE(errno == ECHILD);
}
}

(kamil)