[Ada] Os_Lib: do not call __gnat_kill for Invalid_Pid

2019-07-08  Dmitriy Anisimkov  <anisimko@adacore.com>

gcc/ada/

	* libgnat/s-os_lib.adb: Do not call __gnat_kill for Invalid_Pid.

From-SVN: r273223

gcc/ada/ChangeLog

+2019-07-08  Dmitriy Anisimkov  <anisimko@adacore.com>
+
+	* libgnat/s-os_lib.adb: Do not call __gnat_kill for Invalid_Pid.
+
 2019-07-08  Piotr Trojanek  <trojanek@adacore.com>
 
 	* sem_util.adb (Enclosing_Package_Or_Subprogram): Do not expect

gcc/ada/libgnat/s-os_lib.adb

@@ -1629,10 +1629,12 @@ package body System.OS_Lib is
       pragma Import (C, C_Kill, "__gnat_kill");
 
    begin
-      if Hard_Kill then
-         C_Kill (Pid, SIGKILL, 1);
-      else
-         C_Kill (Pid, SIGINT, 1);
+      if Pid /= Invalid_Pid then
+         if Hard_Kill then
+            C_Kill (Pid, SIGKILL, 1);
+         else
+            C_Kill (Pid, SIGINT, 1);
+         end if;
       end if;
    end Kill;