clang/test/Misc/permissions.cpp: Suppress this on MSYS with the feature 'shell-preserves-root'.

FIXME: Could we introduce another feature for it?

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@185797 91177308-0d34-0410-b5e6-96231b3b80d8