site: set nanosleep() behaviour for glibc / musl

site: set nanosleep() behaviour for glibc / musl

As per coreutils' (gnulib's) autotools test, nanosleep()
misbehaves on glibc (2.29), and works fine on musl.

During cross-compile, recent coreutils assume brokenness
when compiling for linux, which pessimises musl.

Set the correct result for musl, and for coherency reasons,
also specify the result for glibc.

Signed-off-by: André Draszik <git@andred.net>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>