TIL: nix develop $(nix eval --raw nixpkgs#pkgsCross.mingwW64.mkShell --apply 's: (s {}).drvPath')

The DLLs shipped are in $LINK_DLL_FOLDERS, so to test with Wine:

x86_64-w64-mingw-gcc ./hello.cpp
# Set the DLL search path; Wine expects semicolons as a separator
WINEPATH="${LINK_DLL_FOLDERS//:/;}" wine ./a.exe