The following user-space program fails to compile:

    #include <linux/socket.h>
    #include <sys/socket.h>
    int main() { return 0; }

The reason is that <linux/socket.h> tests __GLIBC__ to decide whether it
should define various structures and macros that are now defined for
user-space by <sys/socket.h>, but __GLIBC__ is not defined if no libc
headers have yet been included.

It seems safe to drop support for libc 5 now.
Signed-off-by: NBen Hutchings <ben@decadent.org.uk>
Signed-off-by: NBastian Blank <waldi@debian.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>