flang doesnot support  -save-temps option 

The reproduce case is very simple :
```console
$ touch empty.f90
$ flang-new   -c emtpy.f90
# this produce a "emtpy" .o
$ flang-new   -c emtpy.f90   -save-temps=obj -Qn
flang-new: warning: argument unused during compilation: '-Qn'
error: unknown integrated tool '-cc1as'. Valid tools include '-fc1'.
```
It seems it invokes the wrong tool.