BuildSystem: Enable Advanced Linux Sound Architecture (ALSA) in NetBSD.

In the script ./configure, AST_EXT_LIB_CHECK checks for external libraries. Some
libraries do not specify all their dependencies and require additional shared
libraries. In AST_EXT_LIB_CHECK, this is the fifth parameter. However, if a
library is specified there, it must exist on the platform, because ./configure
tries to compile/link/execute a small app using those statements. For example,
the library libdl.so is Linux specific and does not exist on BSD-like platforms.

Furthermore, no supported platform/version was found, which still (ever?)
requires those additional libraries. Therefore, they were simply removed.

Finally, this change adds the error code ESTRPIPE to the channel driver
chan_alsa for those platforms which lack it, again for example NetBSD.

ASTERISK-27720

Change-Id: I3b21f2135f6cbfac7590ccdc2df753257f426e0b

channels/chan_alsa.c

@@ -41,6 +41,10 @@
 
 ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
 
+#include <errno.h>
+#ifndef ESTRPIPE
+#define ESTRPIPE EPIPE
+#endif
 #include <fcntl.h>
 #include <sys/ioctl.h>
 #include <sys/time.h>