[NFC][AMDGPU] Do not override GetDefaultDwarfVersion

[scott.linder]

Summary

Use the implementation inhereted from ToolChain for as long
as we default to Dwarf 4 for every AMDGPU toolchain.

[scott.linder]

No other target overrides GetDefaultDwarfVersion with the same implementation, and in the future when we make changes we can add them at the points in the hierarchy where they make sense semantically.

clang/lib/Driver/ToolChains/AMDGPU.h

const StringRef getOptionDefault(options::ID OptID) const {
     auto opt = OptionsDefault.find(OptID);
     assert(opt != OptionsDefault.end() && "No Default for Option");
     return opt->second;
   }
 
 public:
   AMDGPUToolChain(const Driver &D, const llvm::Triple &Triple,
                   const llvm::opt::ArgList &Args);
-  unsigned GetDefaultDwarfVersion() const override { return 4; }
   bool IsIntegratedAssemblerDefault() const override { return true; }
   bool IsMathErrnoDefault() const override { return false; }
 
   llvm::opt::DerivedArgList *
   TranslateArgs(const llvm::opt::DerivedArgList &Args, StringRef BoundArch,
                 Action::OffloadKind DeviceOffloadKind) const override;
 
   void addClangTargetOptions(const llvm::opt::ArgList &DriverArgs,

clang/lib/Driver/ToolChains/HIP.h

void AddHIPIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                          llvm::opt::ArgStringList &CC1Args) const override;
 
   SanitizerMask getSupportedSanitizers() const override;
 
   VersionTuple
   computeMSVCVersion(const Driver *D,
                      const llvm::opt::ArgList &Args) const override;
 
-  unsigned GetDefaultDwarfVersion() const override { return 4; }
-
   const ToolChain &HostTC;
 
 protected:
   Tool *buildLinker() const override;
 };
 
 } // end namespace toolchains
 } // end namespace driver
 } // end namespace clang
 
 #endif // LLVM_CLANG_LIB_DRIVER_TOOLCHAINS_HIP_H