Add sys$ttyname_r and ttyname_r() + ttyname().

And print a greeting when sh starts up so we know which TTY we're on.

Kernel/Syscall.cpp

@@ -114,6 +114,8 @@ DWORD handle(DWORD function, DWORD arg1, DWORD arg2, DWORD arg3)
         return current->sys$set_mmap_name((void*)arg1, (size_t)arg2, (const char*)arg3);
     case Syscall::PosixReadlink:
         return current->sys$readlink((const char*)arg1, (char*)arg2, (size_t)arg3);
+    case Syscall::PosixTtynameR:
+        return current->sys$ttyname_r((int)arg1, (char*)arg2, (size_t)arg3);
     default:
         kprintf("int0x80: Unknown function %x requested {%x, %x, %x}\n", function, arg1, arg2, arg3);
         break;