stdout: add a simple stdout redirector

stdout.sh

@@ -0,0 +1,12 @@
+#!/bin/sh
+
+# A trivial script that takes an output file as the first argument, an
+# executable as the second, and subsequent arguments. stdout is piped to the
+# output file.
+#
+# This is used to workaround CMake's inflexible output options for custom
+# targets.
+
+dst=$1
+shift 1
+exec $@ > $dst