Since r179283, internal shell is default on windows and so shell-preserves-root

is true on MSYS bash although this requires: used to disable tests on MSYS bash.

Nevertheless, all tests requiring shell-preserves-root do pass except for
Driver/darwin-sdkroot.c. It will require a patch, either by disabling it on 
Windows or by fixing shell-preserves-root to really be true only on MSYS
and making darwin-sdkroot.c its only user.

In any case, all other tests requiring shell-preserves-root do not really require
it so I'm replacing REQUIRES: shell-preserves-root with REQUIRES: shell in two
tests first.

llvm-svn: 242312