env: Fix out of tree building of tools-all

With the move of environment code from common/ to env/ a number of
changes needed to be made to various make targets.  We missed updating
some of the files required for out of tree builds of the tools.  Correct
the 'environ' target to know that we need to work under tools/env/ still
(not tools/environ/) and then update the wrappers in env_attr.c and
env_flags.c to point to the new correct file.

Reported-by: Peter Robinson <pbrobinson@gmail.com>
Tested-by: Peter Robinson <pbrobinson@gmail.com>
Signed-off-by: Tom Rini <trini@konsulko.com>