### Problem
ubuntu-latest was updated to 22.04 which removes clang++-10 we used for
coverage stats and creates a pre-compiled binary that requires a glibc
upgrade https://github.com/Roblox/luau/issues/773
### Solution
Pin to ubuntu-20.04 using multi-value matrix configurations.
In coverage configuration, we use clang++-10 once again.
Github fails to find clang++-10.
Since we install llvm without a specific version number, we shouldn't
use clang++-10 with a version number.
I tried installing llvm-10, but that package is not available on github
(any more?).
This change adds codegen runs to coverage config and adds O2/codegen
testing to CI.
Note that we don't run O2 combinations in coverage - it's better that we
see gaps in O2 coverage in compiler tests, as these are valuable for
validating codegen intricacies that are difficult to see from
conformance tests passing/failing.
We don't need to run any cachegrind benchmarks in benchmark-dev, since
benchmark uses our new callgrind setup instead.
Also removes prototyping filters that we no longer need from all builds.
Changed the GHA workflows to:
- Not run `build` and `release` workflows for PRs that only affect `prototyping/`
- Run `prototyping` workflow when PRs affect `Analysis/**`, `Ast/**`, or the `luau-ast` source files
Attempt to fix coverage builds by using checkout@v2 instead of v1 which might fix the detacthed HEAD issue.
On the off chance it doesn't, add extra logging around git specifically.
We keep getting compat reports for warnings in various compiler
versions. While we can keep merging PRs to resolve these warnings, it
would be nice if the users of other compilers or compiler versions weren't
blocked on us fixing this.
As such, this change disables Werror by default and only enables it when
requested, which happens in CI in test builds.
vegorov-rbx