[clang] [flang] [clang][driver] When -fveclib=ArmPL flag is in use, always link against libamath (PR #116432)

[David Truby via cfe-commits]

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@@ -490,6 +490,16 @@ void tools::AddLinkerInputs(const ToolChain &TC, const InputInfoList &Inputs,
     else
       A.renderAsInput(Args, CmdArgs);
   }
+  if (const Arg *A = Args.getLastArg(options::OPT_fveclib)) {
+    if (A->getNumValues() == 1) {
+      StringRef V = A->getValue();
+      if (V == "ArmPL") {
+        CmdArgs.push_back(Args.MakeArgString("-lamath"));
+        CmdArgs.push_back(Args.MakeArgString("-lm"));
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DavidTruby wrote:

We actually do support this on Windows, I was wrong above. So we should not be breaking this for Windows users.

I suppose the other option is to say that if someone passes `-fveclib=ArmPL` they will also have to pass the right flags to link to ArmPL and libamath themselves, rather than doing anything in the driver automatically? Assuming that's what @paulwalker-arm means, I'd probably agree and say that should be on the user to sort out and not on the driver. 

https://github.com/llvm/llvm-project/pull/116432