Implement a `winsymlinks` mode that prefers native symlinks, falling back to the deep copy mode#114

dscho wants to merge 2 commits intomsys2:msys2-3.5.7msys2/msys2-runtime:msys2-3.5.7from

dscho:native-symlinks-with-deepcopy-fallbackdscho/Cygwin-msys2-fork:native-symlinks-with-deepcopy-fallbackCopy head branch name to clipboard