util: Add numeric CHECK_*_LT() runtime check macros
util: Add numeric CHECK_*_LT() runtime check macros

This implements the CHECK_*_LT() macros, which expand into runtime tests,
and check whether the expression evaluates to a numeric value which is
strictly less-than a given reference number. For example:

  CHECK_U16_LT (16, calculate_some_uint16_value ());

will check that the expression evaluates to a value less-than 16.

aperezdc/lua-eol,aperezdc/eris,aperezdc/lua-eol,aperezdc/eris