See https://github.com/tailscale/tailscale/issues/4924#issuecomment-1168201823
Arch uses a different login binary that makes the -h flag set the PAM
service to "remote". So if they don't have that configured, don't pass -h.
Thanks to @eddiezane for debugging!
Updates #4924
Change-Id: I8d33e0afb2dfb99517bcea2f9d5d0c6247519b3c
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>