[clang] [CUDA] add wrapper header for libc++'s __utlility/declval.h (PR #148918)

[Jordan Rupprecht via cfe-commits]

rupprecht wrote:

LGTM. I would like it if the new file were formatted, but I suppose it's intentional in order to be more of an exact copy of the libc++ file?

https://github.com/llvm/llvm-project/pull/148918