Why does the __cxa_rethrow always increment uncaughtExceptions?

[盏一]

For native exceptions, it is reasonable to increment uncaughtExceptions in __cxa_rethrow because __cxa_begin_catch performs the corresponding decrement operation. However, for foreign exceptions, __cxa_begin_catch does not perform the decrement operation on uncaughtExceptions, and in fact, no function will decrement uncaughtExceptions at this point. This causes uncaughtExceptions to be incremented every time a foreign exception is rethrown, as shown in https://godbolt.org/z/G6fKrjEvM.

On the contrary, clang libc++ only increments uncaughtExceptions for native exceptions:

```
void __cxa_rethrow() {
    __cxa_eh_globals* globals = __cxa_get_globals();
    __cxa_exception* exception_header = globals->caughtExceptions;
    if (NULL == exception_header)
        std::terminate();      // throw; called outside of a exception handler
    bool native_exception = __isOurExceptionClass(&exception_header->unwindHeader);
    if (native_exception)
    {
        exception_header->handlerCount = -exception_header->handlerCount;
        globals->uncaughtExceptions += 1;
    }
    else  // this is a foreign exception
    {
        globals->caughtExceptions = 0;
    }
}
```

Best regards,
盏一