scons: move host build tool to a proper place

This patch aims to move scons host build tool into packages feeds, where
this tools belongs. There are currently no packages in the master tree
which would need scons, yet scons is build always as part of host tools,
just in order to satisfy host build dependency of few packages in the
packages feeeds.

Signed-off-by: Petr Štetiar <ynezz@true.cz>

devel/scons/patches/001-platform_env.patch

@@ -0,0 +1,11 @@
+--- a/engine/SCons/Platform/__init__.py
++++ b/engine/SCons/Platform/__init__.py
+@@ -65,6 +65,8 @@ def platform_default():
+     care about the machine architecture.
+     """
+     osname = os.name
++    if 'PLATFORM' in os.environ:
++        return os.environ['PLATFORM']
+     if osname == 'java':
+         osname = os._osType
+     if osname == 'posix':