Give coreutils a chance to build the df utility

Give coreutils a chance to build the df utility

The coreutils configure script is unable determine how to get free
space from the Operating System when cross-compiling.
This changes caches the result of the "statfs2_bsize" test for the
coreutils configure script.
Both glibc and uclibc defines statfs as a two-argument function
and uses a struct statfs containing a f_bsize field. That's why
the fu_cv_sys_stat_statfs2_bsize variable has to be defined for
both libcs.

(From OE-Core rev: fa1eb21933a880aa20e4ca87574753b1ec272c3b)

Signed-off-by: Julian Pidancet <julian.pidancet@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>