[Flang] Link -lflang_rt.runtime if available on the device (#132737)

Summary:
Now that we can build the Fortran runtime on the GPU (mostly) we should
be able to implicitly link it if it exists. This matches the normal
behavior where it is included implicity. No tests because it
would require a full VFS and is fairly trivial.

---------

Co-authored-by: Michael Kruse <[email protected]>

Author: jhuber6

clang/lib/Driver/ToolChains/Clang.cpp

@@ -9337,6 +9337,11 @@ void LinkerWrapper::ConstructJob(Compilation &C, const JobAction &JA,
         CmdArgs.push_back(
             Args.MakeArgString("--device-linker=" + TC.getTripleString() + "=" +
                                "-lclang_rt.builtins"));
+      bool HasFlangRT = HasCompilerRT && C.getDriver().IsFlangMode();
+      if (HasFlangRT)
+        CmdArgs.push_back(
+            Args.MakeArgString("--device-linker=" + TC.getTripleString() + "=" +
+                               "-lflang_rt.runtime"));
     });
   }