Hide freeMemory et.al. warnings

Marlin/src/HAL/HAL_STM32F1/HAL.h

 #define __bss_end __bss_end__
 
 /** clear reset reason */
-void HAL_clear_reset_source (void);
+void HAL_clear_reset_source(void);
 
 /** reset reason */
-uint8_t HAL_get_reset_source (void);
+uint8_t HAL_get_reset_source(void);
 
 void _delay_ms(const int delay);
 
   return top;
 }
 */
+
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wunused-function"
+
 static int freeMemory() {
   volatile char top;
   return &top - reinterpret_cast<char*>(_sbrk(0));
 }
 
+#pragma GCC diagnostic pop
+
 //
 // SPI: Extended functions which take a channel number (hardware SPI only)
 //
  */
 void eeprom_write_byte(uint8_t *pos, unsigned char value);
 uint8_t eeprom_read_byte(uint8_t *pos);
-void eeprom_read_block (void *__dst, const void *__src, size_t __n);
-void eeprom_update_block (const void *__src, void *__dst, size_t __n);
+void eeprom_read_block(void *__dst, const void *__src, size_t __n);
+void eeprom_update_block(const void *__src, void *__dst, size_t __n);
 
 //
 // ADC

Marlin/src/HAL/HAL_STM32F1/persistent_store_sdcard.cpp

 }
 
 bool PersistentStore::write_data(int &pos, const uint8_t *value, const size_t size, uint16_t *crc) {
-  for (int i = 0; i < size; i++)
+  for (size_t i = 0; i < size; i++)
     HAL_STM32F1_eeprom_content[pos + i] = value[i];
   crc16(crc, value, size);
   pos += size;
 }
 
 bool PersistentStore::read_data(int &pos, uint8_t* value, const size_t size, uint16_t *crc, const bool writing/*=true*/) {
-  for (int i = 0; i < size; i++) {
+  for (size_t i = 0; i < size; i++) {
     uint8_t c = HAL_STM32F1_eeprom_content[pos + i];
     if (writing) value[i] = c;
     crc16(crc, &c, 1);