[clang] [Driver] Handle Flang in same manner between Gnu and *BSD/Solaris ToolChain (PR #70429)

[Brad Smith via cfe-commits]

brad0 wrote:

> Seems fine to me once a test is added:)

I cannot test as is as the frontend does not support these flags yet. I am just keeping things in sync between the C++ bit above that..
```
  if (D.CCCIsCXX() &&
      !Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs,
                   options::OPT_r)) {
```
and the behavior being the same for the other OS's.

But I am working on a patch for the frontend to enable the flags. So I'll just keep this around for a bit and then update it.

https://github.com/llvm/llvm-project/pull/70429