system_rtc_mem_read() (and write) not available in esp8266_RTOS_SDK (GIT8266O-869)

[RexLBrownSr]

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Issue or Suggestion Description

My application uses the deep sleep and I need to have access to the RTC RAM to preserve values during the deep sleep. I have cloned the version of the esp8266_RTOS_SDK at: https://github.com/espressif/ESP8266_RTOS_SDK.git
My application compiles fine except for the functions system_rtc_mem_read() and system_rtc_mem_write().
The code I am using was originally working ok on the arduino ide but I needed to port to the espressif version and these functions do not seem to be supported. What is necessary for me to do in order to get access to these functions?