llvm-git: More tweaks.

llvm-git: More tweaks.

On python3, use bytes for reading and applying the patch file, rather
than str. This fixes encoding issues when applying patches with
python3.X (reported by zturner).

Also, simplify and speed up "svn update" via svn's "--parents"
argument, instead of manually computing and supplying the list of
parent directories to update.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@347766 91177308-0d34-0410-b5e6-96231b3b80d8