Makefile.uk: Add minimum compiler version check

Makefile.uk: Add minimum compiler version check

libcxx 14 relies on some C++ features that are only implemented starting
from GCC 11 and Clang 10.
This change adds an explicit compiler version check to warn the user
about this incompatibility.

Signed-off-by: Andrei Tatar <andrei@unikraft.io>
Reviewed-by: Stefan Jumarea <stefanjumarea02@gmail.com>
Reviewed-by: Maria Sfiraiala <maria.sfiraiala@gmail.com>
Reviewed-by: Radu Nichita <radunichita99@gmail.com>
Approved-by: Razvan Deaconescu <razvand@unikraft.io>
Tested-by: Unikraft CI <monkey@unikraft.io>
GitHub-Closes: #33