[C++ PATCH] Fix build_noexcept_spec ICE (PR c++/54207)

Hi! We ICE on the following testcase, because perform_implicit_conversion_flags doesn't guarantee the type of the returned value is boolean_type_node, if it is some other type compatible with it (in the same_type_p sense), then simple == boolean_true_node and == boolean_false_node comparisons don'

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