You cannot mix different runtimes msvcr*,dll builds together, especially true with C++, since the C++ runtime are very tightly linked to the underlying runtime, and are implemented very differently. If you switched from MSVC 2003 to clang/llvm, you have to recompile too, even if everything is using msvcr71.dll. libc++ is from clang/llvm, not mingw-w64, it is different from msvcp71.dll C++ runtime.
_mingw_mac.h: bump to 13.x
DFP: fix typos and errors caught by GCC 15
That is the source code package, it does not have any binaries. If you are looking for something usable immediately on Windows, use something like MSYS2. The installer includes mingw-w64 and the compiler toolchain programs.
Yes, there aren't any major breaking incompatible changes in the master branch, the project is already quite mature. Most changes are backports from wine header declarations to support newer Windows APIs and support for newer GCC versions rather than on the C startup code itself. mfmediaengine.h was added in November 2023 but 11.0.1 was released in April 2023, it is safe to use the master branch if you want the newer APIs. Looks like there are still some patches that the developers are working on...
There really isn't a planned release cycle. I normally start one when development is relatively quiet. I'll check with the others if there are still working on anything.
__pformat_fpreg_bits: change to match __gdtoa prototype
That's correct, in terms of cross compiler compatibility, there is no reason to be compatible since C++ is a complex enough language to have vastly different implementations underneath.