Add kyberslash patches for valgrind-based constant-time testing

[pablo-gf]

This PR includes Valgrind's Kyberslash patch for the ubuntu-latest container so that the constant-time tooling framework from PR #2449 can be included in CI, as discussed in a previous status call.

Let me know if you have any comments or suggestions before moving it to ready for review!

[baentsch]

Is this image meant to completely replace the valgrind build in the liboqs PR? If I'm not mistaken, that one's matrixed on the compiler, but I don't see this here: Intentional?

[pablo-gf]

Thanks for the comment @baentsch. Yes, this image completely replaces the building process of the kyberslash-patched Valgrind in the liboqs PR. The matrix compiler (gcc vs clang) is only used to build and test liboqs (not Valgrind) via the ./ct_test.sh script. In the original workflow, the Valgrind build step didn't actually reference the matrix compiler, so Valgrind itself was already being built with the default system compiler.

The idea is that the container will directly include the Kyberslash-patched version of Valgrind, and we can execute the CT tests directly calling valgrind_varlat following the architecture set by the job's matrix (compiler, liboqs build, optimization flag).

Hope that clarifies it, but maybe I misunderstood your comment. Please let me know if that's the case.

[baentsch]

Hope that clarifies it

It does. Then this PR LGTM. Thanks for streamlining things, @pablo-gf

[bhess]

LGTM