package/xfsprogs: disable crc32selftest

xfsprogs generates a crc32 table, and wants to test it. So it builds a
native crc32selftest binary. So far, so good; except the host may not
have the required headers (uuid/uuid.h), and probably libs (like
libuuid).

And anyway, testing the table on the host is flawed, as it does not mean
it would be correct on the target (due to differences in bitness,
endianness, alignment...).

So we just disable the crc32selftest for Buildroot.

Fixes:
    http://autobuild.buildroot.org/results/5d0/5d0ed24b4d368fed100bc3c4959520ebaa48e693/
    http://autobuild.buildroot.org/results/aef/aef223ee2646599eaab7c82f63ff5f19569d69a5/
    http://autobuild.buildroot.org/results/fb6/fb6679f3b1473169702c303ee5060abe7559b0b3/


    ....

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>