Update link to gcc documentation on AT 12.0
Update link to gcc documentation on AT 12.0

There is no documentation for the current version of gcc8, 8.2.1.
The link has been updated to refer to the version 8.2.0 which has
documention.

Signed-off-by: Erwan Prioul <9949cc68615082c237e6af925cacbd2ea7f2e953@linux.ibm.com>

advancetoolchain/advance-toolchain,advancetoolchain/advance-toolchain,advancetoolchain/advance-toolchain,advancetoolchain/advance-toolchain,advancetoolchain/advance-toolchain,advancetoolchain/advance-toolchain