Align struct passwd definition with other variations of libc

Add pg_gecos ("real name") field to struct passwd.

Bug: 14679430
Bug: 12875898
Change-Id: I833ec2c46f6a6259b7232a8e3f7942968ef0b50d
diff --git a/libc/include/pwd.h b/libc/include/pwd.h
index 6f3fad5..6d483c0 100644
--- a/libc/include/pwd.h
+++ b/libc/include/pwd.h
@@ -100,12 +100,15 @@
 
 struct passwd
 {
-    char* pw_name;
-    char* pw_passwd;
-    uid_t pw_uid;
-    gid_t pw_gid;
-    char* pw_dir;
-    char* pw_shell;
+  char* pw_name;
+  char* pw_passwd;
+  uid_t pw_uid;
+  gid_t pw_gid;
+#ifdef __LP64__
+  char* pw_gecos;
+#endif
+  char* pw_dir;
+  char* pw_shell;
 };
 
 __BEGIN_DECLS