Fixes three tests failing on Windows:
```
Swift(windows-x86_64) :: ModuleInterface/ModuleCache/force-module-loading-mode-archs.swift
Swift(windows-x86_64) :: ModuleInterface/ModuleCache/force-module-loading-mode-framework.swift
Swift(windows-x86_64) :: ModuleInterface/ModuleCache/force-module-loading-mode.swift
```
These test cases remove read access to the `.swiftmodule` . The expected
behavior is that the compiler checks `fs.exists("path-to.swiftmodule")`
, determines that the file exists and chooses to use it instead of the
`.swiftinterface`. Compilation then fails because the file cannot be
read.
e22cf2e993/lib/Frontend/ModuleInterfaceLoader.cpp (L752)
On Windows, we were denying `R` access, which is broader than only read
access to file contents but also includes file attributes and
permissions. This caused `fs.exists` to fail since it relies on
`fs.status`, which could not open the file with `CreateFileW`. The fix
is is to only deny `RD - read data/list directory` access.
Make `make-unreadable` python 3 compatible. `POINTER` is now in
`ctypes` rather than in `ctypes.wintypes`. Use the new location which
is compatible across python 2 and python 3.
