fix: Fixing lots of compilation warnings

- fix(esp8266):
  - Adding includes for missing symbols.
  - Removing unused variables.
  - Skip unsupported packing pragmas.
  - Add rom_functions.h for symbols that come from the ESP ROM. Add attributes on
ets_printf so GCC will check the syntax of the formatting string and types of
the arguments.
  - Add ETS_GPIO_INTR_EN(DIS)ABLE macro.
  - Use gpio_output_conf instead of gpio_output_set.

- fix(freertos):
  - Define functions that are useful.
  - Use correct printf symbols when printing.

- fix(lwip):
  - Ignore the warning in sntp.

- fix(mqtt):
  - `xTicksToWait` is unsigned, can't check for less than zero. Remove
unused variables.

- fix(newlib):
  - `_free_r()` returns `void`, not `void *`.
  - Adding includes for missing symbols.

- fix(ssl):
  - Make sure functions always return a value.

Merges https://github.com/espressif/ESP8266_RTOS_SDK/pull/188

components/esp8266/include/driver/gpio.h

@@ -29,6 +29,10 @@
 extern "C" {
 #endif
 #include "esp8266/gpio_register.h"
+
+#define ETS_GPIO_INTR_ENABLE()  _xt_isr_unmask(1 << ETS_GPIO_INUM)
+#define ETS_GPIO_INTR_DISABLE() _xt_isr_mask(1 << ETS_GPIO_INUM)
+
 #define GPIO_Pin_0              (BIT(0))  /* Pin 0 selected */
 #define GPIO_Pin_1              (BIT(1))  /* Pin 1 selected */
 #define GPIO_Pin_2              (BIT(2))  /* Pin 2 selected */