Failed build with MSVC: error C2668 callcc: ambiguous call to overloaded function

[Saigut]

Boost version: 1.72.0
MSVC Version: 19.20.x
Compiler error log:

xxx\include\boost/context/continuation_fcontext.hpp(325): error C2668: 'boost::context::callcc': ambiguous call to overloaded function
xxx\include\boost/context/fiber_fcontext.hpp(212): note: could be 'boost::context::fiber boost::context::callcc<boost::context::fixedsize_stack,_Ty>(std::allocator_arg_t,StackAlloc &&,Fn &&)'
        with
        [
            _Ty=cppt_co0::<lambda_b1a1exxxxx>,
            StackAlloc=boost::context::fixedsize_stack,
            Fn=cppt_co0::<lambda_b1a1exxxxx>
        ]
xxx\include\boost/context/continuation_fcontext.hpp(332): note: or 'boost::context::continuation boost::context::callcc<boost::context::fixedsize_stack,_Ty>(std::allocator_arg_t,StackAlloc &&,Fn &&)'
        with
        [
            _Ty=cppt_co0::<lambda_b1a1exxxxx>,
            StackAlloc=boost::context::fixedsize_stack,
            Fn=cppt_co0::<lambda_b1a1exxxxx>
        ]

This error maybe introduced from this commit 10d3264#diff-05a991caec6cc800bb08467c92d4e2bf99390853e78b0c173247624b14978f16.
The two callcc member functons in fiber class seem should to be deleted.

[olk]

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