Use target_words_bigendian() instead of an ifdef.

Remove CONFIG_RISCV_DIS from the check for riscv as a host; this is
a poisoned identifier, and anyway will always be set by meson.build
when building on a riscv host.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20230508133745.109463-3-thuth@redhat.com>
[rth: Type change done in a separate patch]
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>