Upgrade to GCC 10.5.0 on master

[deadwood2]

Thanks to hard work of @thatguywiththekids we now have an updated version of GCC on master branch, for both x86_64 and m68k targets!

During work on upgrade we discovered that our auto-generated headers in 'inline' and 'defines' directories are not compatible with new GCC and had to be re-implemented. As a result, if you are using a local build and you update sources to latest version you need to do a one-time full rebuild, that is:

1. re-build toolchain
2. re-build your target

You can use the ./rebuild.sh script as always to execute these actions. No additional parameters are needed as GCC 10.5.0 is now the default. Remember that ./rebuild.sh script completely deletes target directory first, so backup whatever you need first.

If you have any questions, please post them in this thread.