[clang] [clang] Implement __builtin_stdc_rotate_left, __builtin_stdc_rotate_right (PR #160259)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

In general, we need a urem anyway: the builtin takes an arbitrary width integer for the rotate amount, but the LLVM IR intrinsic requires that the shift amount has the same width as the value to be rotated.

In some cases we can maybe optimize out the urem.

https://github.com/llvm/llvm-project/pull/160259