feat: do not overwrite the CMAKE_CXX_STANDARD if it exists

Author: tishion

CMakeLists.txt

@@ -78,7 +78,11 @@ set(CMAKE_C_STANDARD 11)
 
 # C++ standard
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
-set(CMAKE_CXX_STANDARD 17)
+if(NOT DEFINED CMAKE_CXX_STANDARD)
+  #set(CMAKE_CXX_STANDARD 14) # 93 - 104
+  set(CMAKE_CXX_STANDARD 17) # 105+
+  #set(CMAKE_CXX_STANDARD 20) # 145+
+endif()
 
 set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/output/$<CONFIG>/bin)
 set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/output/$<CONFIG>/lib)