pbio/platform/essential_hub: Don't optimize firmware info away.
Fixes
@@ -38,7 +38,7 @@ typedef struct {
// defined in linker script
extern const uint32_t _checksum;
-const lego_fw_info_t __attribute__((section(".fw_info"))) fw_info = {
+const lego_fw_info_t __attribute__((section(".fw_info"), used)) fw_info = {
// These values are not used.
.fw_ver = PBIO_VERSION_STR,
.checksum = &_checksum,
