Remove obsolete traces of checking/defining cxx_std_17

frmts/tiledb/CMakeLists.txt

@@ -16,7 +16,6 @@ if(TARGET gdal_TileDB_core)
     target_include_directories(gdal_TileDB_core PRIVATE $<TARGET_PROPERTY:TileDB::tiledb_shared,INTERFACE_INCLUDE_DIRECTORIES>)
     target_compile_definitions(gdal_TileDB_core PRIVATE $<TARGET_PROPERTY:TileDB::tiledb_shared,INTERFACE_COMPILE_DEFINITIONS>)
     target_compile_definitions(gdal_TileDB_core PRIVATE -DTILEDB_DEPRECATED=)
-    target_compile_features(gdal_TileDB_core PRIVATE cxx_std_17)
 endif()
 
 if(NOT TARGET gdal_TileDB)

port/CMakeLists.txt

@@ -52,6 +52,7 @@ set(CPL_SOURCES
     cplstring.cpp
     cpl_vsisimple.cpp
     cpl_vsil.cpp
+    cpl_vsi_mem.cpp
     cpl_http.cpp
     cpl_hash_set.cpp
     cplkeywordparser.cpp
@@ -130,19 +131,6 @@ if(CMAKE_INSTALL_FULL_SYSCONFDIR)
     target_compile_definitions(cpl PRIVATE SYSCONFDIR="${CMAKE_INSTALL_FULL_SYSCONFDIR}")
 endif()
 
-# To enable conditional use of std::shared_mutex in cpl_vsi_mem.cpp
-add_library(cpl_vsi_mem OBJECT cpl_vsi_mem.cpp)
-target_sources(${GDAL_LIB_TARGET_NAME} PRIVATE $<TARGET_OBJECTS:cpl_vsi_mem>)
-target_compile_options(cpl_vsi_mem PRIVATE ${GDAL_CXX_WARNING_FLAGS} ${WFLAG_OLD_STYLE_CAST} ${WFLAG_EFFCXX})
-set_property(TARGET cpl_vsi_mem PROPERTY POSITION_INDEPENDENT_CODE ${GDAL_OBJECT_LIBRARIES_POSITION_INDEPENDENT_CODE})
-target_include_directories(cpl_vsi_mem PRIVATE ${CMAKE_CURRENT_SOURCE_DIR} ${CMAKE_CURRENT_BINARY_DIR})
-
-include(CheckCXXCompilerFlag)
-check_cxx_compiler_flag("-std=c++17" COMPILER_SUPPORTS_CXX17)
-if(COMPILER_SUPPORTS_CXX17)
-    target_compile_features(cpl_vsi_mem PRIVATE cxx_std_17)
-endif()
-
 if (WIN32)
   target_sources(cpl PRIVATE cpl_vsil_win32.cpp)
 else ()