tools: Partially revert "Cross-compilation fixes."

tools: Partially revert "Cross-compilation fixes."

This partially reverts commit 16504669c5cbb8b195d20412aadc838da5c428f7.

Doesn't look like much of 16504669c5cbb8b195d20412aadc838da5c428f7
actually remains due to passage of time.

Of the 3, both Python and pygrub appear to mostly be building just fine
cross-compiling.  The OCAML portion is being troublesome, this is going
to cause bug reports elsewhere soon.  The OCAML portion though can
already be disabled by setting OCAML_TOOLS=n and shouldn't have this
extra form of disabling.

Signed-off-by: Elliott Mitchell <ehem+xen@m5p.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
Acked-by: Wei Liu <wl@xen.org>