Add new cc and c++ tests to check whether UBSan works.
These tests are prepared for GCC (in base) and Clang (with external patches).
Enable these tests for all ports by default, just verify whether we are
using GCC/Clang or a compatible compiler.
Add five equivalent C and C++ tests:
- Integer addition overflow
- Integer divide by zero
- Integer negation overflow
- Integer subtraction overflow
- VLA out of bounds
All tests pass on NetBSD/amd64.
Patch submitted by <Harry Pantazis>
Minor cleanup by <myself>
e308425ef5