ss7.c: Redirecting incorrect sys/poll.h to poll.h

[InterLinked1]

When musl is used, such as on Alpine Linux, there is a warning about redirecting sys/poll.h to poll.h:

gcc -g -Wall -Werror -Wstrict-prototypes -Wmissing-prototypes -fPIC -O2  -MD -MT ss7.o -MF .ss7.o.d -MP -c -o ss7.o ss7.c
In file included from ss7.c:39:
/usr/include/sys/poll.h:1:2: error: #warning redirecting incorrect #include <sys/poll.h> to <poll.h> [-Werror=cpp]
    1 | #warning redirecting incorrect #include <sys/poll.h> to <poll.h>
      |  ^~~~~~~
cc1: all warnings being treated as errors
make: *** [Makefile:176: ss7.o] Error 1