cmake: Fix building for macOS with Xcode generator (thanks, dungaipar…

…a!).

Fixes Bugzilla #3625.

CMakeLists.txt

@@ -433,11 +433,15 @@ if(USE_GCC OR USE_CLANG)
     list(APPEND EXTRA_CFLAGS "-Wshadow")
   endif()
 
-  set(CMAKE_REQUIRED_FLAGS "-Wl,--no-undefined")
-  check_c_compiler_flag("" HAVE_NO_UNDEFINED)
-  set(CMAKE_REQUIRED_FLAGS ${ORIG_CMAKE_REQUIRED_FLAGS})
-  if(HAVE_NO_UNDEFINED)
-    list(APPEND EXTRA_LDFLAGS "-Wl,--no-undefined")
+  if(APPLE)
+    list(APPEND EXTRA_LDFLAGS "-Wl,-undefined,error")
+  else()
+    set(CMAKE_REQUIRED_FLAGS "-Wl,--no-undefined")
+    check_c_compiler_flag("" HAVE_NO_UNDEFINED)
+    set(CMAKE_REQUIRED_FLAGS ${ORIG_CMAKE_REQUIRED_FLAGS})
+    if(HAVE_NO_UNDEFINED)
+      list(APPEND EXTRA_LDFLAGS "-Wl,--no-undefined")
+    endif()
   endif()
 endif()