MINGW-packages: C++ hello world is causing a segmentation fault

I just updated all MSYS2 packages on one of my machines, then tried to recompile some of my C++ programs, and noticed that several of them are giving a segmentation fault. I was able to simplify the issue a lot. Here is a shell session in a MinGW-w64 64-bit Shell showing how I can recreate the problem by trying to compile a simple C++ program. Can anyone else reproduce this?

$ cat prog.cpp
#include <iostream>

int main(int argc, char ** argv)
{
    std::cout << "Hello world." << std::endl;
    return 1;
}

$ g++ prog.cpp -o prog.exe

$ ./prog.exe
Segmentation fault

$ gdb ./prog.exe
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Reading symbols from ./prog.exe...done.
(gdb) run
Starting program: C:\Users\David\Documents\scraps\test_c++\prog.exe
[New Thread 116908.0x1c420]

Program received signal SIGSEGV, Segmentation fault.
0x000000006fcae829 in ?? () from D:\msys64\mingw64\bin\libstdc++-6.dll
(gdb) where
#0  0x000000006fcae829 in ?? () from D:\msys64\mingw64\bin\libstdc++-6.dll
#1  0x000000006fcfb2a9 in ?? () from D:\msys64\mingw64\bin\libstdc++-6.dll
#2  0x000000006fd00317 in ?? () from D:\msys64\mingw64\bin\libstdc++-6.dll
#3  0x00000000004015e7 in main ()
(gdb)

If I comment out the line that writes to std::cout, the problem goes away and the executable works.

Some of my C++ programs were able to write to their output without having a segmentation fault, so I might look into this further to see what the difference is between a working program and a failing program.