[Driver][NFC] Remove some redundant code in Driver.cpp.

[Jimerlife]

Summary

options::OPT_target has been done in Driver::BuildCompilation, so I think this part of code is redundant.

[Jimerlife]

ping...

[MaskRay]

computeTargetTriple has several users. You probably want to check all these code paths do not need if (const Arg *A = Args.getLastArg(options::OPT_target)).
For the uses in BuildCompilation, it seems fine.

clang/lib/Driver/Driver.cpp

 /// Compute target triple from args.
 ///
 /// This routine provides the logic to compute a target triple from various
 /// args passed to the driver and the default triple string.
 static llvm::Triple computeTargetTriple(const Driver &D,
                                         StringRef TargetTriple,
                                         const ArgList &Args,
                                         StringRef DarwinArchName = "") {
-  // FIXME: Already done in Compilation *Driver::BuildCompilation
-  if (const Arg *A = Args.getLastArg(options::OPT_target))
-    TargetTriple = A->getValue();
-
   llvm::Triple Target(llvm::Triple::normalize(TargetTriple));
 
   // GNU/Hurd's triples should have been -hurd-gnu*, but were historically made
   // -gnu* only, and we can not change this, so we have to detect that case as
   // being the Hurd OS.
   if (TargetTriple.contains("-unknown-gnu") || TargetTriple.contains("-pc-gnu"))
     Target.setOSName("hurd");