Add killpg(3).

libc/Makefile

@@ -224,6 +224,7 @@ poll/poll.o \
 poll/ppoll.o \
 pwd/pwent.o \
 signal/kill.o \
+signal/killpg.o \
 signal/psignal.o \
 signal/raise.o \
 signal/sigaction.o \

libc/signal/killpg.cpp

@@ -0,0 +1,30 @@
+/*******************************************************************************
+
+    Copyright(C) Jonas 'Sortie' Termansen 2013.
+
+    This file is part of the Sortix C Library.
+
+    The Sortix C Library is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Lesser General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or (at your
+    option) any later version.
+
+    The Sortix C Library is distributed in the hope that it will be useful, but
+    WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+    or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
+    License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with the Sortix C Library. If not, see <http://www.gnu.org/licenses/>.
+
+    signal/killpg.cpp
+    Send signal to a process group.
+
+*******************************************************************************/
+
+#include <signal.h>
+
+extern "C" int killpg(pid_t pgid, int signum)
+{
+	return kill(-pgid, signum);
+}