fixes

esphome/components/ota/ota_backend_arduino_rp2040.cpp

@@ -20,8 +20,8 @@ OTAResponseTypes ArduinoRP2040OTABackend::begin(size_t image_size) {
   // Handle UPDATE_SIZE_UNKNOWN (0) by calculating available space
   if (image_size == 0) {
     // Similar to ESP8266, calculate available space from flash layout
-    extern uint8_t _FS_start;
-    extern uint8_t _FS_end;
+    extern "C" uint8_t _FS_start;
+    extern "C" uint8_t _FS_end;
     // Calculate the size of the filesystem area which will be used for OTA
     size_t fs_size = &_FS_end - &_FS_start;
     // Reserve some space for filesystem overhead

esphome/components/web_server/ota/ota_web_server.cpp

@@ -203,4 +203,4 @@ void WebServerOTAComponent::dump_config() {
 }  // namespace web_server
 }  // namespace esphome
 
-#endif  // USE_WEBSERVER_OTA
+#endif  // USE_WEBSERVER_OTA

esphome/components/web_server/ota/ota_web_server.h

@@ -23,4 +23,4 @@ class WebServerOTAComponent : public ota::OTAComponent {
 }  // namespace web_server
 }  // namespace esphome
 
-#endif  // USE_WEBSERVER_OTA
+#endif  // USE_WEBSERVER_OTA