Improve MinGW support.

- Code specific to Windows was #ifdef'ed with _MSC_VER so it wasn't included with MinGW. So _MSC_VER is replaced with _WIN32.
- MinGW doesn't support _get_pgmptr() so it is necessary to directly call the Win32 function GetModuleFileName(). This implies including windows.h which in turn causes a name clash with the Win32 function SearchPath(). So the cc65 type SearchPath is renamed to SearchPaths.

src/sim65/paravirt.c

@@ -36,15 +36,18 @@
 #include <string.h>
 #include <stdlib.h>
 #include <fcntl.h>
+#if defined(_WIN32)
+#  define O_INITIAL O_BINARY
+#else
+#  define O_INITIAL 0
+#endif
 #if defined(_MSC_VER)
 /* Microsoft compiler */
 #  include <io.h>
 #  pragma warning(disable : 4996)
-#  define O_INITIAL O_BINARY
 #else
 /* Anyone else */
 #  include <unistd.h>
-#  define O_INITIAL 0
 #endif
 
 /* common */