Prefer POSIX getpgrp() to getpgid(0).

We use getpgrp() in most place so prefer it for consistency
with the rest of the code base.

Author: millert

lib/util/getentropy.c

@@ -470,7 +470,7 @@ getentropy_fallback(void *buf, size_t len)
 			HX((pid = getpid()) == -1, pid);
 			HX((pid = getsid(pid)) == -1, pid);
 			HX((pid = getppid()) == -1, pid);
-			HX((pid = getpgid(0)) == -1, pid);
+			HX((pid = getpgrp()) == -1, pid);
 			HX((e = getpriority(0, 0)) == -1, e);
 
 			if (!faster) {

src/sudo.c

@@ -537,7 +537,7 @@ get_user_info(struct user_details *ud)
 
     ud->pid = getpid();
     ud->ppid = getppid();
-    ud->pgid = getpgid(0);
+    ud->pgid = getpgrp();
     ttyfd = open(_PATH_TTY, O_RDWR);
     sudo_get_ttysize(ttyfd, &ud->ts_rows, &ud->ts_cols);
     if (ttyfd != -1) {