WIP: SDK: Add experimental backport of gcc 9, g++ 9
- SDK: Add experimental backport of gcc 9, g++ 9. This is a single monolithic package, always behaves as though it was invoked with -static-libgcc -static-libstdc++, and always uses the pre-existing backport of binutils-2.30. (T21481)
- tests: Check that gcc 9, g++ 9 work correctly
- tests: Fix shellcheck warnings
Edited by Simon McVittie