dump: Simplify compiling win_dump.o by introducing win_dump_available()

dump: Simplify compiling win_dump.o by introducing win_dump_available()

To make dump.c less target dependent, move the TARGET_X86_64 #ifdef'ry
from dump.c to win_dump.c (introducing a win_dump_available() method
there). By doing so we can build win_dump.c on any target, and
simplify the meson rule.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20230225094903.53167-5-philmd@linaro.org>