sunaudio: don't compile in the sun audio backend if sys/audioio.h is missing.

Newer Solaris-based releases, like OpenIndiana, don't include this, using
Open Sound System, or something layered over OSS like PulseAudio, instead.

Fixes #13405.

configure

@@ -28741,12 +28741,22 @@ printf "%s\n" "#define SDL_VIDEO_DRIVER_ANDROID 1" >>confdefs.h
         if test x$enable_audio = xyes; then
           case $ARCH in
             sysv5|solaris|hpux)
+                                ac_fn_c_check_header_compile "$LINENO" "audio/audiolib.h" "ac_cv_header_audio_audiolib_h" "$ac_includes_default"
+if test "x$ac_cv_header_audio_audiolib_h" = xyes
+then :
+  have_sys_audiolib=yes
+else $as_nop
+  have_sys_audiolib=no
+fi
+
+                if test x$have_sys_audiolib = xyes; then
 
 printf "%s\n" "#define SDL_AUDIO_DRIVER_SUNAUDIO 1" >>confdefs.h
 
-                SOURCES="$SOURCES $srcdir/src/audio/sun/*.c"
-                SUMMARY_audio="${SUMMARY_audio} sun"
-                have_audio=yes
+                    SOURCES="$SOURCES $srcdir/src/audio/sun/*.c"
+                    SUMMARY_audio="${SUMMARY_audio} sun"
+                    have_audio=yes
+                fi
             ;;
             netbsd)  # Don't use this on OpenBSD, it's busted.