use _Static_assert()

the Keil compiler with some compiler options doesn't have
static_assert(), and the MRS compiler suite seems to have the same
issue

Src/main.c

@@ -359,8 +359,9 @@ uint16_t low_cell_volt_cutoff = 330; // 3.3volts per cell
 
 //=========================== END EEPROM Defaults ===========================
 
+
 const char filename[30] __attribute__((section(".file_name"))) = FILE_NAME;
-static_assert(sizeof(FIRMWARE_NAME) <=13,"Firmware name too long");   // max 12 character firmware name plus NULL 
+_Static_assert(sizeof(FIRMWARE_NAME) <= 13,"Firmware name too long");   // max 12 character firmware name plus NULL
 
 uint8_t EEPROM_VERSION;
 // move these to targets folder or peripherals for each mcu