[SimplifyLibCalls] Constant fold nan libcall (#101459)
Reference: https://en.cppreference.com/w/c/numeric/math/nan
The logic is copied from clang frontend:
https://github.com/llvm/llvm-project/blob/1d2b2d29d733200b704f38d220d22ecc07d6cf42/clang/lib/AST/ExprConstant.cpp#L14741-L14777
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Co-authored-by: Nikita Popov <github@npopov.com>
