unbound: Tweak freebsd-configure script

Regenerating the configure script is optional and can introduce noise
if the installed versions of autoconf, automake, and libtool do not
match those used upstream.  Tweak our script slightly so it will skip
this step if libtoolize is not found.

contrib/unbound/freebsd-configure.sh

@@ -14,7 +14,7 @@ unbound=$(dirname $(realpath $0))
 cd $unbound
 
 # Run autotools before we drop LOCALBASE out of PATH
-(cd $unbound && libtoolize --copy && autoheader && autoconf)
+libtoolize --copy && autoheader && autoconf
 
 # Ensure we use the correct toolchain and clean our environment
 export CC=$(echo ".include <bsd.lib.mk>" | make -f /dev/stdin -VCC)