busybox

Config: select PLATFORM_LINUX if using sendfile()

Man entry for sendfile:

  Not specified in POSIX.1-2001, or other standards.

  Other UNIX systems implement sendfile() with different  semantics  and
  prototypes. It should not be used in portable programs.

Select PLATFORM_LINUX if enabling FEATURE_USE_SENDFILE.

Signed-off-by: Bartosz Golaszewski <bartekgola@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>