[clang] [flang] [driver] Generalize the code that adds the path of libflang_rt.runtime.a. (PR #134362)

[Fangrui Song via cfe-commits]

================
@@ -850,6 +852,21 @@ void ToolChain::addFortranRuntimeLibraryPath(const llvm::opt::ArgList &Args,
     CmdArgs.push_back(Args.MakeArgString("-L" + DefaultLibPath));
 }
 
+void ToolChain::addFlangRTLibPath(const ArgList &Args,
+                                  llvm::opt::ArgStringList &CmdArgs) const {
+  // Link static flang_rt.runtime.a or shared flang_rt.runtime.so
----------------
MaskRay wrote:

```
Link static flang_rt.runtime.a or shared flang_rt.runtime.so.
On AIX, default to static flang-rt.
```

https://github.com/llvm/llvm-project/pull/134362