[clang] [ubsan] Remove -fsanitizer=vptr from -fsanitizer=undefined (PR #121115)

[Oliver Hunt via cfe-commits]

ojhunt wrote:

This obviously cases https://github.com/llvm/llvm-project/issues/143065

@AaronBallman @erichkeane @zygoloid commented in the RFC - this change regresses the checks in ubsan for default compilation modes in order to make the use of sanitize=undefined easier in non-default scenarios.

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