[llvm-branch-commits] [ubsan] Remove -fsanitizer=vptr from -fsanitizer=undefined (PR #121115)

[Vitaly Buka via llvm-branch-commits]

https://github.com/vitalybuka created https://github.com/llvm/llvm-project/pull/121115

This makes `undefined` more consistent.

`vptr` check adds additional constraints:
1. rtti is no, or compilation error
2. c++abi, or linking error
3. trap is off,  or silently disabled

So it's not obvious if `-fsanitizer=undefined`
will have it on.