linux-user/syscall.c: remove wrong forward decl of setgroups()

this declaration is wrong:
the correct prototype on linux is:
int setgroups(size_t size, const gid_t *list);

since by default musl libc exposes this symbol in unistd.h
additionally to grp.h, the wrong declaration causes a build error.

the proper fix is to simply include the correct header.
Signed-off-by: NJohn Spencer <maillist-qemu@barfooze.de>
Reviewed-by: NStefan Weil <sw@weilnetz.de>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

linux-user/syscall.c

@@ -28,6 +28,7 @@
 #include <fcntl.h>
 #include <time.h>
 #include <limits.h>
+#include <grp.h>
 #include <sys/types.h>
 #include <sys/ipc.h>
 #include <sys/msg.h>
@@ -584,7 +585,6 @@ extern int personality(int);
 extern int flock(int, int);
 extern int setfsuid(int);
 extern int setfsgid(int);
-extern int setgroups(int, gid_t *);
 
 /* ARM EABI and MIPS expect 64bit types aligned even on pairs or registers */
 #ifdef TARGET_ARM