Looking to make a GDC-12 mingw64 package

[Chris Piker]

Hi GDC

I've been able to build gdc-12.1 on ubuntu20 using
```
wget 
http://mirrors.concertpass.com/gcc/releases/gcc-12.1.0/gcc-12.1.0.tar.xz
tar -xvf gcc-12.1.0.tar.xz
cd gcc-12.1.0
mkdir build
cd build
../configure --prefix=/usr/local/gcc12 --enable-languages=d \
   --enable-libphobos-checking --disable-multilib 
--program-suffix=-12
make -j6
make install
```

Now I'm looking to repeat the process for mingw64.  I see that 
I'll need an older version of gdc first, say 11.3.  So that's 
okay, I'll build it twice, but in general I'm wondering if:

   1. Anyone has built gdc-11 in the mingw64 environment since it 
seems a few patches are required?

   2. How we might go about creating a pacman package for gdc-12 
since it requires an existing D compiler?

The first one is just an information request since the old 
PKGBUILD files are on github, but the second one is a bit more 
daunting.  Without a previous version of gdc to build gdc it 
might be hard to get a mingw64 package accepted.

Thanks