Revert "GCC: Upgrade to version 9.2-2019.12 of toolchain"

This reverts commit de9bf1d8a2de952bfc17cdf7082b41f9c185e54d.

Change-Id: Iebb6297ce290a10ee850bf6a9c71e7eb530b085f
diff --git a/docs/plat/meson-gxbb.rst b/docs/plat/meson-gxbb.rst
index f891ecd..2cd8342 100644
--- a/docs/plat/meson-gxbb.rst
+++ b/docs/plat/meson-gxbb.rst
@@ -17,7 +17,7 @@
 
 .. code:: shell
 
-    CROSS_COMPILE=aarch64-none-elf- make DEBUG=1 PLAT=gxbb bl31
+    CROSS_COMPILE=aarch64-linux-gnu- make DEBUG=1 PLAT=gxbb bl31
 
 This port has been tested in a ODROID-C2. After building it, follow the
 instructions in the `U-Boot repository`_, replacing the mentioned **bl31.bin**