[clang] [Driver] Link Flang runtime on Solaris (PR #65644)

[Rainer Orth via cfe-commits]

rorth wrote:

> > I wonder how to proceed with the patch at hand.
> 
> I'm not a Solaris expert, but based on this discussion I'd consider adding support for `-fuse-ld` in Flang. This sort of changes are often as simple as updating Options.td. Same for `-r`.

Support of `-fuse-ld` is not Solaris-specific in any way.  Other targets support e.g. `-fuse-ld=[bfd|lld]`.  That would be just another case of Flang needing to support common flags.  However, I don't understand how Flang option handling is done, unfortunately.  Whatever the case, this is an issue separate from this patch: the only reason we were talking about `-r` and friends is that my patch guards adding the Flang runtime libs with `! -nostdlib && ! -nodefaultlibs && ! -r`, which I believe we have now established is correct.

However, Flang accepts none of those options yet, which it should for compatiblity with both `clang++` and `gfortran`.  However, I won't be able to deal with any of this: I've quite a number of other issues on my plate.

> One important rule of thumb that I'd stick to:
> 
>     * Do whatever Clang, GFortran and GCC do.
> 
> 
> In cases where there's different behavior between these compilers, just go for whatever feels most sensible, but please document your design decision.

Fully agreed: I've now checked that gfortran handles all of `-r`, `-nostdlib`, and `-nodefaultlibs`, so I believe `flang-new` should follow suite.


https://github.com/llvm/llvm-project/pull/65644