cmake: fix detection of library functions when -Werror is enabled.

(Reference issue: https://github.com/libsdl-org/SDL/issues/7011)

CMakeLists.txt

@@ -466,23 +466,6 @@ set_option(SDL_INSTALL_TESTS   "Install test-cases" OFF)
 
 set(HAVE_STATIC_PIC "${SDL_STATIC_PIC}")
 
-if(SDL_WERROR)
-  if(MSVC)
-    check_c_compiler_flag(/WX HAVE_WX)
-    if(HAVE_WX)
-      set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} /WX")
-      set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /WX")
-    endif()
-  elseif(USE_GCC OR USE_CLANG)
-    check_c_compiler_flag(-Werror HAVE_WERROR)
-    if(HAVE_WERROR)
-      set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Werror")
-      set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Werror")
-      set(CMAKE_OBJC_FLAGS "${CMAKE_OBJC_FLAGS} -Werror")
-    endif()
-  endif()
-endif()
-
 if(SDL_HIDAPI)
   if(HIDAPI_ONLY_LIBUSB)
     set(SDL_HIDAPI_LIBUSB ON CACHE BOOL "" FORCE)
@@ -2836,6 +2819,23 @@ if(NOT HAVE_SDL_TIMERS)
   list(APPEND SOURCE_FILES ${TIMER_SOURCES})
 endif()
 
+if(SDL_WERROR)
+  if(MSVC)
+    check_c_compiler_flag(/WX HAVE_WX)
+    if(HAVE_WX)
+      set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} /WX")
+      set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /WX")
+    endif()
+  elseif(USE_GCC OR USE_CLANG)
+    check_c_compiler_flag(-Werror HAVE_WERROR)
+    if(HAVE_WERROR)
+      set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Werror")
+      set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Werror")
+      set(CMAKE_OBJC_FLAGS "${CMAKE_OBJC_FLAGS} -Werror")
+    endif()
+  endif()
+endif()
+
 # Append the -MMD -MT flags
 # if(DEPENDENCY_TRACKING)
 #   if(COMPILER_IS_GNUCC)