Cygwin and Windows git stopped playing nicely together after a recent Windows update. There’s a variety of recommendations for how to fix this this on StackOverflow and elsewhere, but this post actually makes the most sense. In a nutshell, msys-1.0.dll (installed into your Program Files\Git\bin directory) is not built to be position independent. Use the dll rebaser to get it to load at a new address, like so:
$ rebase.exe -b 0x50000000 msys-1.0.dll
And voila, git goodness restored.