Destroy the variable argument list ap after initialization with va_start (part of the desugaring of ...) or va_copy.

Code generation backends should not provide a custom implementation for this intrinsic. This intrinsic does not map to the LLVM va_end intrinsic.

This function is a no-op on all current targets, but used as a hook for const evaluation to detect UB when a variable argument list is used incorrectly.

Safety

ap must not be used to access variable arguments after this call.