Linux kernel defines EWOULDBLOCK as EAGAIN (since before v2.6.12-rc2).

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210704183755.655002-3-f4bug@amsat.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>