Do not include OSS header

We only need standard system calls to send/get SysEx messages
to/from a MIDI device, so we don't have to include the OSS
soundcard.h header.

configure.ac

@@ -44,10 +44,8 @@ AS_CASE(["x$midi_backend"],
                       [AC_DEFINE([USE_ALSA_MIDI_API], [1],
                                  [Define wether to use the ALSA MIDI API.])])],
         [xoss],
-        [AC_CHECK_HEADERS([soundcard.h],
-                          [AC_DEFINE([USE_OSS_MIDI_API], [1],
-                                     [Define whether to use the OSS MIDI API.])],
-                          [AC_MSG_ERROR([OSS header not found.])])],
+        [AC_DEFINE([USE_OSS_MIDI_API], [1],
+                   [Define whether to use the OSS MIDI API.])],
         [AC_MSG_ERROR([No MIDI backend selected.])])
 
 dnl Output files

src/midi.c

@@ -150,7 +150,6 @@ midi_error(midi_io_t *midi)
 #elif USE_OSS_MIDI_API
 /* Open Sound System MIDI API */
 #include <fcntl.h>
-#include <soundcard.h>
 
 #define MIDI_IO_BUFFER_SIZE 256