mini_al: Support {Net,Open}BSD OSS

Fixes this build failure:
http://www.cpantesters.org/cpan/report/a069fade-0e1f-11e8-a1cf-bb670eaac09d

src/external/mini_al.h

@@ -59,7 +59,7 @@
 //
 // Building (BSD)
 // --------------
-// The BSD build uses OSS and should Just Work without any linking nor include path configuration.
+// BSD build uses OSS. Requires linking to -lossaudio on {Open,Net}BSD, but not FreeBSD.
 //
 // Building (Emscripten)
 // ---------------------
@@ -6712,6 +6712,10 @@ static mal_result mal_device__main_loop__alsa(mal_device* pDevice)
 #include <fcntl.h>
 #include <sys/soundcard.h>
 
+#ifndef SNDCTL_DSP_HALT
+#define SNDCTL_DSP_HALT SNDCTL_DSP_RESET
+#endif
+
 int mal_open_temp_device__oss()
 {
     // The OSS sample code uses "/dev/mixer" as the device for getting system properties so I'm going to do the same.