gn build: Let get.py keep zip file in memory instead of using a temp file

The zip is small, and it's a bit less code this way.
No intended behavior change.

Differential Revision: https://reviews.llvm.org/D59677

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@356884 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed