SystemTools: Adapt permissions test to MSYS

Cygwin/MSYS uses umask on *stat* when noacl is set on the filesystem
(which MSYS sets by default), so the returned permissions don't
necessarily reflect what was actually set.

Solve by delaying umask to where it is actually needed.

testSystemTools.cxx

@@ -292,14 +292,15 @@ static bool CheckFileOperations()
 
   std::cerr << std::oct;
 // Reset umask
-#if defined(_WIN32) && !defined(__CYGWIN__)
+#ifdef __MSYS__
+  mode_t fullMask = S_IWRITE;
+#elif defined(_WIN32) && !defined(__CYGWIN__)
   // NOTE:  Windows doesn't support toggling _S_IREAD.
   mode_t fullMask = _S_IWRITE;
 #else
   // On a normal POSIX platform, we can toggle all permissions.
   mode_t fullMask = S_IRWXU | S_IRWXG | S_IRWXO;
 #endif
-  mode_t orig_umask = umask(fullMask);
 
   // Test file permissions without umask
   mode_t origPerm, thisPerm;
@@ -371,6 +372,7 @@ static bool CheckFileOperations()
     res = false;
   }
 
+  mode_t orig_umask = umask(fullMask);
   // Test setting file permissions while honoring umask
   if (!kwsys::SystemTools::SetPermissions(testNewFile, fullMask, true)) {
     std::cerr << "Problem with SetPermissions (3) for: " << testNewFile