switch statement case label has only `int` template argument

首先定位报告中提到的 switch_statement 和 case_statement 入口点，然后使用所述的编译器行为重现示例。跟踪 case 值和 lambda 参数的类型推导过程；当诸如 2147483648 这样的整数 case 值能够被正确表示并匹配，而不是产生“other”，并且为此行为提供回归测试覆盖时，即表示完成。

Before gcc9, if a template argument is an integral value, no compiler error/warning generated when the specified value is bigger than the integral value MAX.

This leads the following runtime issue:

#include <iostream>

#include <boost/lambda/lambda.hpp>
#include <boost/lambda/switch.hpp>

int main() {
    using namespace boost;
    using namespace boost::lambda;
    
    switch_statement(
        _1,
        case_statement<2147483648>(std::cout << constant("big")),
        default_statement(std::cout << constant("other"))
    )(2147483648); // prints 'other'
    // static_cast<int>(2147483648) is OK
}

This issue prone working can be eliminated in any following way:

• replace case_statement template argument from int to uintmax_t or intmax_t or any bigger than int. This solves that not only int parameters can be accepted in later gcc's and clang too.
• switch_statement lambda accepts/casts argument int. This solves type safety.
• some other template magic, where at case statement can be set the acceptable integral type, and switch statement recognizes, and uses common_type to casts lambda parameter to that.