compiler error on macOS Siera with address@hidden

[Denis Davydov]

Dear developers,

m4 fails to compile on macOS Sierra with GCC:

./sched.h:42:8: error: redefinition of 'struct sched_param'
 struct sched_param
        ^~~~~~~~~~~
In file included from ./sched.h:27:0,
                 from ./spawn.h:37,
                 from execute.c:47:
/usr/include/sched.h:35:8: note: originally defined here
 struct sched_param { int sched_priority;  char __opaque[__SCHED_PARAM_SIZE__]; };
        ^~~~~~~~~~~
make[3]: *** [execute.o] Error 1
make[3]: *** Waiting for unfinished jobs....
In file included from ./spawn.h:37:0,
                 from spawn-pipe.c:47:
./sched.h:42:8: error: redefinition of 'struct sched_param'
 struct sched_param
        ^~~~~~~~~~~
In file included from ./sched.h:27:0,
                 from ./spawn.h:37,
                 from spawn-pipe.c:47:
/usr/include/sched.h:35:8: note: originally defined here
 struct sched_param { int sched_priority;  char __opaque[__SCHED_PARAM_SIZE__]; };
        ^~~~~~~~~~~
make[3]: *** [spawn-pipe.o] Error 1
make[2]: *** [all] Error 2
make[1]: *** [all-recursive] Error 1
make: *** [all] Error 2

Kind regards,

Denis