No exception is thrown when an invalid character range (e.g., [b-a]) is included.

[wkensuke]

Bugzilla Link	51686
Version	12.0
OS	All
CC	@mclow,@utsumi-fj,@wkensuke

Extended Description

---

#include <regex>
#include <cassert>
#include <cstdio>

static bool error_range_thrown(const char *pat)
{
    bool result = false;
    try {
        std::regex re(pat);
    } catch (const std::regex_error &ex) {
        puts("regex_error");
        fflush(stdout);
        result = (ex.code() == std::regex_constants::error_range);
    }   
    return result;
}

int main(int, char**) {
    assert(error_range_thrown("([b-a])"));
}

---

This program is created using the regular expression sample described in the C++ language standard, but it did not throw an exception (as expected).
(e.g., Table 132 in http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/n4713.pdf)

I've confirmed that this problem can be reproduced using clang 13.0.0 "[C++] clang HEAD 13.0.0 (https://github.com/llvm/llvm-project.git c4ed142)" on Wandbox (https://wandbox.org/).
This code throws the exception on gcc-10.1.0 (or other gcc version).