CMake: Use source_groups to represent the source tree

* It let ide's (like vs) display the source tree.
* Disabled by default.
* Soft requirement is cmake >= 2.8.12 .
* Offers 2 modes: flat & hierarchical.
* For detailed description see #14471
* Thanks @click for help and advises.
* Closes #14471

CMakeLists.txt

@@ -50,6 +50,8 @@ endif()
 
 include(CheckPlatform)
 
+include(GroupSources)
+
 # basic packagesearching and setup (further support will be needed, this is a preliminary release!)
 set(OPENSSL_EXPECTED_VERSION 1.0.0)