Fix build errors after modifying CMake setup.h.in

Always set a value to ICONV_CONST so it will be defined in setup.h.
Add a check for strtoull to prevent a macro redefined warning.
Link with WebKit framework to fix macOS build with wxUSE_WEBKIT.

build/cmake/lib/core/CMakeLists.txt

@@ -70,6 +70,11 @@ if(WXOSX_COCOA)
     wx_lib_link_libraries(core PUBLIC
         "-framework AudioToolbox"
         )
+    if(wxUSE_WEBKIT)
+        wx_lib_link_libraries(core PUBLIC
+            "-framework WebKit"
+            )
+    endif()
 endif()
 if(WXGTK AND wxUSE_PRIVATE_FONTS)
     wx_lib_include_directories(core PUBLIC

build/cmake/setup.cmake

@@ -221,6 +221,7 @@ if(NOT WIN32)
     if(wxUSE_LIBICONV AND NOT APPLE)
         find_package(Iconv REQUIRED)
         set(HAVE_ICONV ON)
+        set(ICONV_CONST " ")
         if(ICONV_SECOND_ARGUMENT_IS_CONST)
             set(ICONV_CONST "const")
         endif()
@@ -554,7 +555,7 @@ endforeach()
 # Check various functions
 foreach(func
     fsync
-    snprintf vsnprintf strnlen
+    snprintf vsnprintf strnlen strtoull
     setpriority
     )
     string(TOUPPER ${func} func_upper)