CMake: Remove the code for old CMake versions

CMakeLists.txt

@@ -132,7 +132,6 @@ endif()
 set(DBG $<OR:$<CONFIG:Debug>,$<CONFIG:RelWithDebInfo>>)
 
 if(IPO)
-  if(CMAKE_VERSION VERSION_GREATER 3.9)
   include(CheckIPOSupported)
   check_ipo_supported(RESULT ipo_supported OUTPUT ipo_output)
   if(ipo_supported)
@@ -141,9 +140,6 @@ if(IPO)
   else()
     message(WARNING "IPO is not supported: ${ipo_output}")
   endif()
-  else()
-      message(WARNING "IPO enablement requires CMake 3.9+")
-  endif()
 endif()
 
 if("0${PROJECT_VERSION_PATCH}" GREATER 9)
@@ -263,7 +259,7 @@ if(NOT MSVC AND NOT HAIKU)
     endif()
   endif()
 
-  if(CMAKE_VERSION VERSION_LESS 3.1 OR TARGET_OS STREQUAL "mac")
+  if(TARGET_OS STREQUAL "mac")
     add_cxx_compiler_flag_if_supported(OUR_FLAGS_OWN -std=gnu++17)
   endif()
 
@@ -303,12 +299,10 @@ if(NOT MSVC AND NOT HAIKU)
   endif()
 
   add_cxx_compiler_flag_if_supported(OUR_FLAGS_OWN -Wall)
-  if(CMAKE_VERSION VERSION_GREATER 3.3 OR CMAKE_VERSION VERSION_EQUAL 3.3)
   add_cxx_compiler_flag_if_supported(OUR_FLAGS_OWN
     $<$<COMPILE_LANGUAGE:C>:-Wdeclaration-after-statement>
     -Wdeclaration-after-statement
   )
-  endif()
   add_cxx_compiler_flag_if_supported(OUR_FLAGS_OWN -Wextra)
   add_cxx_compiler_flag_if_supported(OUR_FLAGS_OWN -Wno-psabi) # parameter passing for argument of type ‘__gnu_cxx::__normal_iterator<CCommandProcessorFragment_Vulkan::SMemoryBlock<1>*, std::vector<CCommandProcessorFragment_Vulkan::SMemoryBlock<1>, std::allocator<CCommandProcessorFragment_Vulkan::SMemoryBlock<1> > > >’ changed in GCC 7.1
   add_cxx_compiler_flag_if_supported(OUR_FLAGS_OWN -Wno-unused-parameter)
@@ -360,8 +354,6 @@ function(set_glob VAR GLOBBING EXTS DIRECTORY) # ...
   if(NOT FILES STREQUAL GLOB_RESULT)
     message(AUTHOR_WARNING "${VAR} does not contain every file from directory ${DIRECTORY}")
     set(LIST_BUT_NOT_GLOB)
-    if(POLICY CMP0057)
-      cmake_policy(SET CMP0057 NEW)
     foreach(file ${FILES})
       if(NOT file IN_LIST GLOB_RESULT)
         list(APPEND LIST_BUT_NOT_GLOB ${file})
@@ -383,7 +375,6 @@ function(set_glob VAR GLOBBING EXTS DIRECTORY) # ...
       message(AUTHOR_WARNING "${VAR} is not alphabetically sorted")
     endif()
   endif()
-  endif()
 
   set(${VAR} ${FILES} PARENT_SCOPE)
 endfunction()
@@ -397,19 +388,11 @@ set(CHECKSUM_SRC)
 
 function(set_own_rpath TARGET)
   if(NOT TARGET_OS STREQUAL "windows" AND NOT TARGET_OS STREQUAL "mac")
-    if(CMAKE_VERSION VERSION_GREATER 3.8 OR CMAKE_VERSION VERSION_EQUAL 3.8)
     set_property(TARGET ${TARGET} PROPERTY BUILD_RPATH "$ORIGIN")
-    endif()
     set_property(TARGET ${TARGET} PROPERTY INSTALL_RPATH "$ORIGIN/../lib/ddnet")
   endif()
 endfunction()
 
-if(NOT TARGET_OS STREQUAL "windows" AND NOT TARGET_OS STREQUAL "mac" AND CMAKE_VERSION VERSION_LESS 3.8)
-  if((CLIENT AND (STEAM OR DISCORD_DYNAMIC)) OR ANTIBOT)
-    message(STATUS "Can't set BUILD_RPATH in CMake before 3.8, pass -Wl,-rpath,'$ORIGIN' manually if you wish to emulate this. Or just install a newer version of CMake...")
-  endif()
-endif()
-
 ########################################################################
 # INITIALIZE TARGET LISTS
 ########################################################################
@@ -807,9 +790,6 @@ if(NOT(GTEST_FOUND) AND DOWNLOAD_GTEST)
 
       set(GTEST_LIBRARIES gtest gmock)
       set(GTEST_INCLUDE_DIRS)
-      if(CMAKE_VERSION VERSION_LESS 2.8.11)
-        set(GTEST_INCLUDE_DIRS "${gtest_SOURCE_DIR}/include" "${gmock_SOURCE_DIR}/include")
-      endif()
     endif()
   endif()
 endif()
@@ -3064,8 +3044,6 @@ endif()
 
 if(DEV)
   # Don't generate CPack targets.
-elseif(CMAKE_VERSION VERSION_LESS 3.6 OR CMAKE_VERSION VERSION_EQUAL 3.6)
-  message(WARNING "Cannot create CPack targets, CMake version too old. Use CMake 3.6 or newer.")
 else()
   set(EXTRA_ARGS DESTINATION ${CPACK_PACKAGE_FILE_NAME} COMPONENT portable EXCLUDE_FROM_ALL)
   install(TARGETS ${CPACK_TARGETS} ${EXTRA_ARGS})
@@ -3295,11 +3273,9 @@ foreach(target ${TARGETS_LINK})
 endforeach()
 
 foreach(target ${TARGETS_OWN})
-  if((CMAKE_VERSION VERSION_GREATER 3.1 OR CMAKE_VERSION VERSION_EQUAL 3.1))
   set_property(TARGET ${target} PROPERTY CXX_STANDARD 17)
   set_property(TARGET ${target} PROPERTY CXX_STANDARD_REQUIRED ON)
   set_property(TARGET ${target} PROPERTY CXX_EXTENSIONS OFF)
-  endif()
 
   if(MSVC)
     target_compile_options(${target} PRIVATE /wd4244) # Possible loss of data (float -> int, int -> float, etc.).