[clang] [Clang][CodeGen] Emit “trap reasons” on UBSan traps (PR #145967)

[Dan Liew via cfe-commits]

delcypher wrote:

@PiJoules 

> There's a large number of tests. Many of these look like they're close to an existing test ... in these cases is it possible to just use the existing test file and add checks under a prefix?

I originally recommended that @anthonyhatran write new tests so this is on me. We'll take a look and see if adding to existing tests is worth it.

FWIW In general I'm actually not a fan of adding to existing tests to avoid tests becoming large, unwieldy, and annoying to debug when they fail. I prefer individual tests to test as few things as possible. As with many things, context is really important so we'll take a look.

https://github.com/llvm/llvm-project/pull/145967