* Migrate all add_definitions to target_compile_definitions
* Remove -D from preprocessor definitions added by target_compile_definitions (unneccessary, cmake strips it anyway)
* Fixed NO_BUFFERPOOL not being set on g3d if jemalloc is used
* Moved library/compiler specific compile flag settings spread all over various CMakeLists to their related library/compiler file
* Remove ancient manual link flag settings for worldserver
* Remove the usage of global flags and definitions
set through the CMAKE_CXX_FLAGS variable.
* Use cmake target compile features for setting the
CXX standard automatically.
* Make C++14 globally available in the project
* Closes#21033
(cherry picked from commit e60c1f84a7)
