glob: Hook in win32 implementation for _MSC_VER.

I'm flying blind here so I don't know if this will actually work, but
I copied the cmake part from src/strife.

src/CMakeLists.txt

@@ -93,6 +93,11 @@ set(GAME_SOURCE_FILES
     w_merge.c           w_merge.h
     z_zone.c            z_zone.h)
 
+if(MSVC)
+    list(APPEND GAME_SOURCE_FILES
+         "../../win32/win_opendir.c" "../../win32/win_opendir.h")
+endif()
+
 set(DEHACKED_SOURCE_FILES
                         deh_defs.h
     deh_io.c            deh_io.h

src/i_glob.c

@@ -16,16 +16,20 @@
 // to be interrogated.
 //
 
-// TODO: Merge win_opendir.[ch] into this file for MSVC implementation.
-
 #include <stdlib.h>
 
 #include "i_glob.h"
 #include "m_misc.h"
 #include "config.h"
 
-#ifdef HAVE_DIRENT_H
-#include "dirent.h"
+// For Visual C++, we need to include the win_opendir module.
+#if defined(_MSC_VER)
+#include <win_opendir.h>
+#elif defined(HAVE_DIRENT_H)
+#include <dirent.h>
+#endif
+
+#if defined(_MSC_VER) || defined(HAVE_DIRENT_H)
 
 struct glob_s
 {