mksh: build in build/ dir; enable SIGCHLD

To build in mksh/build/ directory use:

  TARGET_OS=Jehanne CC=x86_64-jehanne-gcc CPPFLAGS="-g -ggdb -gdwarf-2 -O0" sh ../src/Build.sh -r

cross/pkgs/mksh/build/init_libc.c

@@ -0,0 +1,26 @@
+/*
+ * This file is part of Jehanne.
+ *
+ * Copyright (C) 2017 Giacomo Tesio <giacomo@tesio.it>
+ *
+ * This is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, version 3 of the License.
+ *
+ * Jehanne 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Jehanne.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include <u.h>
+#include <libc.h>
+#include <posix.h>
+
+void
+__application_newlib_init(void)
+{
+	libposix_emulate_SIGCHLD();
+}