Add build for the minimal version described at Documentation/process/changes.rst

Reported by @mchehab

IMO, it could make sense to also run:

    make drivers/media drivers/staging/media

For the minimal compiler version listed at:

    Documentation/process/changes.rst

e. g.:

    ====================== ===============  ========================================
            Program        Minimal version       Command to check the version
    ====================== ===============  ========================================
    GNU C                  5.1              gcc --version
    Clang/LLVM (optional)  11.0.0           clang --version

Although rare, we had in the past reports from breakages with older toolchains.

No need to do full builds or multiple builds there. Just allyesconfig is probably enough.