Enable automatic build support on FreeBSD

Thanks-to: <royj@yandex.ru>

libs/libzrtp/configure.in

@@ -24,7 +24,6 @@ case $target_os in
   ;;
   *freebsd2* | *freebsd* | *netbsd* | *openbsd* | *osf[12]*)
   echo "------- START libzrtp configuration for BSD platform ------------"
-  AC_DEFINE(PLATFORM,ZP_BSD,BSD platform)
   ;;
   hpux* | irix* | linuxaout* | linux* | osf* | solaris2* | sunos4*)
   echo "------- START libzrtp configuration for Linux platform ------------"

libs/libzrtp/include/zrtp_config.h

@@ -19,6 +19,8 @@
 #if !defined(ZRTP_PLATFORM)
 #	if defined(ANDROID_NDK)
 #		define ZRTP_PLATFORM ZP_ANDROID
+#	elif defined(__FreeBSD__)
+#		define ZRTP_PLATFORM ZP_BSD
 #	elif defined(linux) || defined(__linux)
 #		include <linux/version.h>
 #		define ZRTP_PLATFORM ZP_LINUX