sb: Add support to search for a suitable version of python.

The command python has been removed from upstream python and python2
and python3 is now used. This patch wraps the commands in a shell
script that locates a suitable python to run.

Updates #3537

source-builder/sb/cmd-defaults.py

@@ -0,0 +1,29 @@
+#
+# RTEMS Tools Project (http://www.rtems.org/)
+# Copyright 2010-2013 Chris Johns (chrisj@rtems.org)
+# All rights reserved.
+#
+# This file is part of the RTEMS Tools package in 'rtems-tools'.
+#
+# Permission to use, copy, modify, and/or distribute this software for any
+# purpose with or without fee is hereby granted, provided that the above
+# copyright notice and this permission notice appear in all copies.
+#
+# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+# OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
+from __future__ import print_function
+
+import sys, os
+
+try:
+    import options
+    options.run(sys.argv)
+except ImportError:
+    print("Incorrect Source Builder installation", file = sys.stderr)
+    sys.exit(1)