Don't use C++17 features

[oneraynyday]

C++17 features cause buildkite to fail.

clang-tools-extra/clang-cast/Matcher.h

Matcher::Matcher(const std::string &FilenameSuffix, const bool Pedantic,
   for (unsigned i = 0; i != FixOptions.size(); i++) {
     FixMask |= FixOptions[i];
   }
 }
 
 // TODO: Is this okay to do?
 Matcher::~Matcher() {
   if (PublishSummary) {
-    for (auto const &[CXXCastKind, Freq] : Statistics) {
+    for (const auto &Pair : Statistics) {
+      const auto &CXXCastKind = Pair.first;
+      const auto &Freq = Pair.second;
       if (!Freq)
         continue;
       llvm::errs() << "The type " << cppCastToString(CXXCastKind)
                    << " has been issued " << Freq
                    << " times throughout the translation unit.\n";
     }
     if (FixMask) {
       llvm::errs() << "The following files were modified:\n";