[NFC] Minor cleanup to use default setting of getLastArg()

[maxim-kuvyrkov]

Summary

Noticed this while I was looking at linker defaults.

[maxim-kuvyrkov]

Fixed thinko: GetLastArg -> GetLastArgValue

[asl]

Looks trivial enough for post-commit review :)

[maxim-kuvyrkov]

The patch was wrong. We use "const Arg *A" at the end of GetLinkerPath, so can't remove it. I thought I tested this, but, apparently, not.

Reverted in 62948c4532d59b59f63409eae5d7f9e4990e5626 .

[asl]

Indeed! And even worse, there is another 'A' shadowing definition below :)

clang/lib/Driver/ToolChain.cpp

std::string ToolChain::GetLinkerPath(bool *LinkerIsLLD,
                                      bool *LinkerIsLLDDarwinNew) const {
   if (LinkerIsLLD)
     *LinkerIsLLD = false;
   if (LinkerIsLLDDarwinNew)
     *LinkerIsLLDDarwinNew = false;
 
   // Get -fuse-ld= first to prevent -Wunused-command-line-argument. -fuse-ld= is
   // considered as the linker flavor, e.g. "bfd", "gold", or "lld".
-  const Arg* A = Args.getLastArg(options::OPT_fuse_ld_EQ);
-  StringRef UseLinker = A ? A->getValue() : CLANG_DEFAULT_LINKER;
+  StringRef UseLinker = Args.getLastArgValue(options::OPT_fuse_ld_EQ,
+               CLANG_DEFAULT_LINKER);
 
   // --ld-path= takes precedence over -fuse-ld= and specifies the executable
   // name. -B, COMPILER_PATH and PATH and consulted if the value does not
   // contain a path component separator.
   if (const Arg *A = Args.getLastArg(options::OPT_ld_path_EQ)) {
     std::string Path(A->getValue());
     if (!Path.empty()) {
       if (llvm::sys::path::parent_path(Path).empty())