LibC: Make sysbeep return int instead of void

Since the beep syscall may fail it is strange that the error is
discarded by the LibC wrapper.

Userland/Libraries/LibC/unistd.h

@@ -34,7 +34,7 @@ int get_process_name(char* buffer, int buffer_size);
 int set_process_name(const char* name, size_t name_length);
 void dump_backtrace();
 int fsync(int fd);
-void sysbeep();
+int sysbeep();
 int gettid();
 int getpagesize();
 pid_t fork();