Reduce temporary directory name length, fixes #2502

Instead of:
C:\Users\Ganesh\AppData\Local\Temp\data-default-instances-old-locale-0.0.1-11924\data-default-instances-old-locale-0.0.1
we get:
C:\Users\Ganesh\AppData\Local\Temp\data-default-instances-old-locale-0.0.1-11924

Instead of:
dist\build\libHSdata-default-instances-old-locale-0.0.1-6jcjjaR25tK4x3nJhHHjFM.a-11924\libHSdata-default-instances-old-locale-0.0.1-6jcjjaR25tK4x3nJhHHjFM.a
we get:
dist\build\objs-11924\libHSdata-default-instances-old-locale-0.0.1-6jcjjaR25tK4x3nJhHHjFM.a

This should put us under the limit.

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>