Reduce raw string pointers usage.

* Change some functions to take `std::string` instead of
  `const char*` in the following classes: `cmMakeFile`, `cmake`,
  `cmCoreTryCompile`, `cmSystemTools`,  `cmState`, `cmLocalGenerator`
  and a few others.
* Greatly reduce using of `const char*` overloads for
  `cmSystemTools::MakeDirectory` and `cmSystemTools::RelativePath`.
* Remove many redundant `c_str()` conversions throughout the code.

Source/cmAddExecutableCommand.cxx

@@ -99,7 +99,7 @@ bool cmAddExecutableCommand::InitialPass(std::vector<std::string> const& args,
       return false;
     }
 
-    const char* aliasedName = s->c_str();
+    std::string const& aliasedName = *s;
     if (this->Makefile->IsAlias(aliasedName)) {
       std::ostringstream e;
       e << "cannot create ALIAS target \"" << exename << "\" because target \""