[Support] Fix some warnings when self-hosting clang on Windows

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186413 91177308-0d34-0410-b5e6-96231b3b80d8
Create files with mode 666. This matches the behavior of other unix tools.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186414 91177308-0d34-0410-b5e6-96231b3b80d8