UserspaceEmulator: Fail sys$map_time_page() with ENOSYS for now

This allows LibC to fall back to sys$clock_gettime() until we can
add support for the kernel time page to UserspaceEmulator.

Userland/DevTools/UserspaceEmulator/Emulator_syscalls.cpp

@@ -247,6 +247,8 @@ u32 Emulator::virt_syscall(u32 function, u32 arg1, u32 arg2, u32 arg3)
         return virt$msyscall(arg1);
     case SC_futex:
         return virt$futex(arg1);
+    case SC_map_time_page:
+        return -ENOSYS;
     default:
         reportln("\n=={}==  \033[31;1mUnimplemented syscall: {}\033[0m, {:p}", getpid(), Syscall::to_string((Syscall::Function)function), function);
         dump_backtrace();