don't link deprecated ossaudio on OpenBSD

Index: CMakeLists.txt
--- CMakeLists.txt.orig
+++ CMakeLists.txt
@@ -366,12 +366,12 @@ ENDIF(WANT_OGGVORBIS)
 
 
 # check whether to enable OSS-support
-IF(LMMS_HAVE_SOUNDCARD_H OR LMMS_HAVE_SYS_SOUNDCARD_H)
+IF(!LMMS_BUILD_OPENBSD AND (LMMS_HAVE_SOUNDCARD_H OR LMMS_HAVE_SYS_SOUNDCARD_H))
 	SET(LMMS_HAVE_OSS TRUE)
 	SET(STATUS_OSS "OK")
 ELSE(LMMS_HAVE_SOUNDCARD_H OR LMMS_HAVE_SYS_SOUNDCARD_H)
 	SET(STATUS_OSS "<not found or not supported on this platform>")
-ENDIF(LMMS_HAVE_SOUNDCARD_H OR LMMS_HAVE_SYS_SOUNDCARD_H)
+ENDIF(!LMMS_BUILD_OPENBSD AND (LMMS_HAVE_SOUNDCARD_H OR LMMS_HAVE_SYS_SOUNDCARD_H))
 
 
 # check for ALSA
