Build system: Raise warning level

Default esp-idf builds now show -Wextra warnings (except for a few:
signed/unsigned comparison, unused parameters, old-style C declarations.)

CI building of examples runs with that level raised to -Werror, to catch
those changes going into the main repo.

components/bootloader_support/src/esp_image_format.c

@@ -17,7 +17,7 @@
 #include <esp_log.h>
 #include <bootloader_flash.h>
 
-const static char *TAG = "esp_image";
+static const char *TAG = "esp_image";
 
 #define SIXTEEN_MB 0x1000000
 #define ESP_ROM_CHECKSUM_INITIAL 0xEF