The function is called with alignment == 0 which caused an assertion.
Use the code from oslib-posix.c to fix that regression.

Fixes: ed6f53f9
Signed-off-by: Stefan Weil <sw@weilnetz.de>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20210611105846.347954-1-sw@weilnetz.de>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>