classes/base: prefer gnu-prefixed HOSTTOOLS

classes/base: prefer gnu-prefixed HOSTTOOLS

Ubuntu 25.10 has changed the default coreutils implementation from GNU
coreutils to uutils/coreutils. Unfortunately this causes build problems:

  couldn't allocate absolute path for 'null'.
  tail: cannot open 'standard input' for reading: No such file or directory
  install: failed to chown '...': Invalid argument (os error 22)

Clear build failures happen in 'install' and 'tail', but there may be
further breakage.

Luckily, Ubuntu also installs GNU coreutils with a binary prefix of
'gnu', so whilst these issues are root-caused and fixed in either pseudo
or uutils we can prefer the gnu-prefixed binaries where they are present.

[ YOCTO #16028 ]

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>