[clang] [SYCL] Disable RTTI for SYCL device code (PR #68020)

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elizabethandrews wrote:

Without the diagnostic we have downstream, this change causes a seg fault when using dynamic_cast in kernel code. It passes without error without this change (although technically it shouldn't be allowed). 

I'm marking this PR as draft till I can work on upstreaming the diagnostic we have downstream as well. 

https://github.com/llvm/llvm-project/pull/68020