I’m moving from mac to PC environment and converting everything the mac did to the PC.
One of the most important aspects is the unix environment.
While running my local deployment script, I ran into multiple problems. One involved running out of PIDs, solved by running the ash shell and running /bin/rebaseall.
Now, PIL is choking on the error gcc: vfork: Resource temporarily unavailable
The solution that worked for me is from this post:
http://cygwin.com/ml/cygwin/2007-01/msg00498.html
Run the following:
rebase -b 0x1000000000 /bin/tk84.dll
And your pip install PIL will work…
Magic.
Yuji Tomita 
THANK YOU!
After days of trying, it finally works now…
Congrats! This is a super annoying issue but it sounds like it is a non trivial problem for Cygwin.
I’m not sure if you’re using Django, but you just prompted me to write a post about my solution to how due to the same issue the Django development server sometimes quits and is super slow.