Meta: modernize old-fashioned loops to range-based for.

Changes done via `clang-tidy` with some manual fine-tuning
for the variable naming and `auto` type deduction
where appropriate.

Source/cmAddCompileOptionsCommand.cxx

@@ -13,9 +13,8 @@ bool cmAddCompileOptionsCommand::InitialPass(
     return true;
   }
 
-  for (std::vector<std::string>::const_iterator i = args.begin();
-       i != args.end(); ++i) {
-    this->Makefile->AddCompileOption(i->c_str());
+  for (std::string const& i : args) {
+    this->Makefile->AddCompileOption(i.c_str());
   }
   return true;
 }