GNAT LLVM Xtensa 20.2 2020-02-28

• Update dependencies to consistently build for Clang 9.0.1
• Fixes "The offset bit width does not match DL specification." bugbox

GNAT LLVM XTensa 20.2

GNAT 20.2 LLVM frontend with XTensa backend suitable for ESP32 and ESP8266 chips.