misc: do not use "tar cf - |tar xf -"

Using this: tar cf - -C "/some/place" |tar xf - -C "/some/other/place"
to copy a directory to another place does not properly fail (when it does).

Using this instead: cp -av "/some/place" "/some/other/place"
makes it easy to see why and how it failed.

Impacted:
libc/uClibc
debug/ltrace
tools/sstrip
scripts/populate

# Compute s390-specific values

CT_DoArchTupleValues() {

    # That's the only thing to override

    if [ "${CT_ARCH_64}" = "y" ]; then

        CT_TARGET_ARCH="s390x"

    fi

}