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

[Rainer Orth via cfe-commits]

rorth wrote:

I'd argue that handling the Flang runtime libs like C++ is the right thing to do here.  However, `flang-new` currently rejects all of `-r`, `-nostdlib`, and `-nodefaultlibs` on both Linux and Solaris.  On top of that, Solaris `clang` doesn't handle `-r` correctly, passing `-e _start -Bdynamic` to `ld`, which makes it choke...

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