-Wtautological-compare should flag tautological pointer bounds checks

[nikic]

-Wtautological-compare should report pointer "bounds checks" patterns that are always true/false because unsigned pointer arithmetic cannot overflow.

bool test1(const char *ptr, size_t index) {
  return ptr + index < ptr; // always false
}

bool test2(const char *ptr, size_t index) {
  return ptr + index >= ptr; // always true
}

These two are fine though:

bool test3(const char *ptr, ssize_t index) {
  return ptr + index < ptr; // unknown (same as index < 0)
}

bool test4(const char *ptr, ssize_t index) {
  return ptr + index >= ptr; // unknown (same as index >= 0)
}

Idea from #118472 (comment).