opendreambox: various fixes and version changes

opendreambox: various fixes and version changes

use gcc4 as compiler for powerpc based stbs (enigma still needs a patch
for this though),
set PREFERRED_VERSION_linux-libc-headers to 2.6.12.0 (it's the correct
version currently, set for mipsel anyways and enigma does not like a
newer one currently),
remove PREFERRED_VERSION_glibc* from dreambox-powerpc since it uses
eglibc now,
comment out PREFERRED_VERSION_busybox in dreambox-powerpc as 1.01
is no longer present and 1.11.3 seems to work fine,
remove bogus PREFERRED_PROVIDER_linux-libc-headers