Yield before reading from zaptel timing source under Solaris so that other threads get a chance to do things. (issue #7875 reported by bob)

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.2@51512 65c4cc65-6c06-0410-ace0-fbb531ad65f3

res/res_musiconhold.c

@@ -45,6 +45,9 @@
 #endif
 #include <unistd.h>
 #include <sys/ioctl.h>
+#ifdef SOLARIS
+#include <thread.h>
+#endif
 
 #include "asterisk.h"
 
@@ -508,6 +511,9 @@ static void *monmp3thread(void *data)
 			}
 		}
 		if (class->pseudofd > -1) {
+#ifdef SOLARIS
+			thr_yield();
+#endif
 			/* Pause some amount of time */
 			res = read(class->pseudofd, buf, sizeof(buf));
 			pthread_testcancel();