Revert "remove unused io.h include"

This reverts commit cb485806c3. Fixes #491.

CMakeLists.txt

@@ -201,6 +201,7 @@ if ( WIN32 )
 
   # Check presence of MS include files
   check_include_file ( windows.h HAVE_WINDOWS_H )
+  check_include_file ( io.h HAVE_IO_H )
   check_include_file ( dsound.h HAVE_DSOUND_H )
   check_include_files ( "windows.h;mmsystem.h" HAVE_MMSYSTEM_H )
 

src/config.cmake

@@ -43,6 +43,9 @@
 /* Define to 1 if you have the <inttypes.h> header file. */
 #cmakedefine HAVE_INTTYPES_H @HAVE_INTTYPES_H@
 
+/* Define to 1 if you have the <io.h> header file. */
+#cmakedefine HAVE_IO_H @HAVE_IO_H@
+
 /* whether or not we are supporting lash */
 #cmakedefine HAVE_LASH @HAVE_LASH@
 

src/utils/fluidsynth_priv.h

@@ -106,6 +106,10 @@
 #include <omp.h>
 #endif
 
+#if HAVE_IO_H
+#include <io.h>
+#endif
+
 #if HAVE_SIGNAL_H
 #include <signal.h>
 #endif