CMake: Add variable to indicate if c++11 or later is enabled

Use it in macOS checks.

build/cmake/functions.cmake

@@ -77,12 +77,7 @@ endmacro()
 function(wx_set_common_target_properties target_name)
     cmake_parse_arguments(wxCOMMON_TARGET_PROPS "DEFAULT_WARNINGS" "" "" ${ARGN})
 
-    if(DEFINED wxBUILD_CXX_STANDARD AND NOT wxBUILD_CXX_STANDARD STREQUAL COMPILER_DEFAULT)
-        if(
-            APPLE AND
-            CMAKE_OSX_DEPLOYMENT_TARGET VERSION_LESS 10.9 AND
-            (wxBUILD_CXX_STANDARD EQUAL 11 OR wxBUILD_CXX_STANDARD EQUAL 14)
-          )
+    if(APPLE AND CMAKE_OSX_DEPLOYMENT_TARGET VERSION_LESS 10.9 AND wxHAS_CXX11)
         if(CMAKE_GENERATOR STREQUAL "Xcode")
             set_target_properties(${target_name} PROPERTIES XCODE_ATTRIBUTE_CLANG_CXX_LIBRARY libc++)
         else()
@@ -90,7 +85,6 @@ function(wx_set_common_target_properties target_name)
             target_link_libraries(${target_name} PRIVATE "-stdlib=libc++")
         endif()
     endif()
-    endif()
     set_target_properties(${target_name} PROPERTIES
         LIBRARY_OUTPUT_DIRECTORY "${wxOUTPUT_DIR}${wxPLATFORM_LIB_DIR}"
         ARCHIVE_OUTPUT_DIRECTORY "${wxOUTPUT_DIR}${wxPLATFORM_LIB_DIR}"

build/cmake/init.cmake

@@ -11,6 +11,11 @@
 if(DEFINED wxBUILD_CXX_STANDARD AND NOT wxBUILD_CXX_STANDARD STREQUAL COMPILER_DEFAULT)
     set(CMAKE_CXX_STANDARD ${wxBUILD_CXX_STANDARD})
 endif()
+if(NOT CMAKE_CXX_STANDARD EQUAL 98)
+    set(wxHAS_CXX11 TRUE)
+else()
+    set(wxHAS_CXX11 FALSE)
+endif()
 
 if(MSVC)
     # Determine MSVC runtime library flag

build/cmake/setup.cmake

@@ -23,11 +23,7 @@ include(CheckTypeSize)
 include(CMakePushCheckState)
 include(TestBigEndian)
 
-if(
-    APPLE AND
-    CMAKE_OSX_DEPLOYMENT_TARGET VERSION_LESS 10.9 AND
-    (CMAKE_CXX_STANDARD EQUAL 11 OR CMAKE_CXX_STANDARD EQUAL 14)
-  )
+if(APPLE AND CMAKE_OSX_DEPLOYMENT_TARGET VERSION_LESS 10.9 AND wxHAS_CXX11)
     set(CMAKE_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS} "-stdlib=libc++")
 endif()