[libc++] Make sure the cin/wcin tests run on remote hosts

When running on remote hosts, we need the whole `echo 123 | %t.exe` command
to run on the remote host. Thus, we need to escape the pipe to make sure
the command is treated as `{ echo 123 | %t.exe } > %t.out` instead of
`{ echo 123 } | %t.exe > %t.out`m where only `echo 123` is run on the
remote host.