Compilation with x86_64-w64-mingw32-g++

[rlpires]

I have put together a patch for 2.2.2 to make it compile with x86_64-w64-mingw32-g++/gcc and target Windows.
Currently using capnp 0.8.0.

Patch is restricted to mmap/munmap and memcpy wrapper.

Some tests throw exceptions, whereas the same on Linux/gcc runs fine.

MINGW64 ~/dev/Mash-2.2.2/test
$ ../mash sketch -o genomes.msh genome1.fna genome2.fna genome3.fna
$ ../mash sketch -r -I reads reads1.fastq reads2.fastq -o reads.msh
$ ../mash dist genomes.msh reads.msh > genomes.dist

This application has requested the Runtime to terminate it in an unusual way.
Please contact the application's support team for more information.
terminate called after throwing an instance of 'kj::ExceptionImpl'
what(): capnp/layout.c++:2384: failed: expected expectedDataBitsPerElement <= dataSize; Message contained list with incompatible element type.

Anyone ever attempted compilation with MinGW?
Thanks.