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/cmCoreTryCompile.h

@@ -33,7 +33,7 @@ protected:
    * This way we do not have to rely on the timing and
    * dependencies of makefiles.
    */
-  void CleanupFiles(const char* binDir);
+  void CleanupFiles(std::string const& binDir);
 
   /**
    * This tries to find the (executable) file created by