Comment 0 for bug 1879481

As done for gcc-7 and gcc-8 in 18.04 LTS in LP: #1848319, I'd like to update the gcc-9 and gcc-10 packages in focal to the final 10.1.0 release.

 - gcc-10, update to the gcc-10.1.0 release
 - gcc-9, update to the gcc-9 release branch to the time
   of the gcc-10 release.
 - corresponding gcc-cross packages

The package builds are prepared in
https://launchpad.net/~doko/+archive/ubuntu/toolchain/+packages

[Impact]
Provide an upstream release for GCC 10.1, and an update for GCC 9 to the 9.3
branch

FIXME: update after the test rebuild is done.

[Regression Potential]
There is regression potential, however with a test rebuild of the main portion of the archive no regressions were found.

[Test Case]
No regressions in the GCC test suite, and no regressions in the test
rebuild of the main component of the archive (all architectures)

As a test, a complete archive rebuild was performed, and no regressions were found with this new package. The archive rebuild also contained updated versions of gcc-9, gcc-10, python3.8, and python3-stdlib-extensions. The GCC and Python packages should not infer with each other.

[Validation]
Analyze the build logs for regressions.
For the cross builds, just make sure that the packages build using
the updated sources.

Summary of the test rebuilds:
https://people.canonical.com/~doko/ftbfs-report/test-rebuild-20191107-bionic-bionic.html
https://people.canonical.com/~doko/ftbfs-report/test-rebuild-20191107-bionic-gcc7-bionic.html

The first one is a reference build, the second one the test rebuild with the updated components.

There are no additional regressions except for one Python test, which sometimes hangs on the buildds, sometimes passes (test_ttk_guionly). Will
be disabled in a follow-up upload.