[libc] Add a linux-x86_64-Release-Asserts fullbuild CI job (#236096)
Currently, none of the hosted Linux fullbuild CI jobs run tests with
assertions enabled: the Debug job only builds tests (`testing: BUILD`),
and the Release jobs build with `-DNDEBUG`. (The monolithic premerge
Linux job builds with `LLVM_ENABLE_ASSERTIONS=ON`, but only tests the
overlay configuration.)
This patch adds a new `linux-x86_64-Release-Asserts` job, which is the
same as `linux-x86_64-Release`, but with `LLVM_ENABLE_ASSERTIONS=ON`.
The new job doesn't build the fuzzing tests, as those are already
covered by
the regular Release job.
Assisted-by: Gemini