fix a libtonezone detection issue on FreeBSD

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@23704 65c4cc65-6c06-0410-ace0-fbb531ad65f3

configure.ac

@@ -185,7 +185,7 @@ fi
 if test "x${PBX_OSTYPE}" = "xLinux" ; then
    AST_EXT_LIB([tonezone], [tone_zone_find], [linux/zaptel.h], [ZAPTEL], [Zaptel])
 else
-   AST_EXT_LIB([tonezone], [tone_zone_find], [zaptel.h], [ZAPTEL], [Zaptel])
+   AST_EXT_LIB([tonezone], [tone_zone_find], [zaptel.h], [ZAPTEL], [Zaptel], [-lm])
 fi
 
 GSM_INTERNAL="yes"