add comments that AC_USE_SYSTEM_EXTENSIONS and AST_PROG_LD

do not work on FreeBSD - presumably they depend on some
auto* feature that is not installed by default.

I am not sure on what is a proper fix. In my local copy
i simply comment them out.

The AST_PROG_LD is a long standing isse, there were attempts
to fix it in the past but probably not enough has been copied
to acinclude.m4, and i had forgotten about it because i
commented out this call in configure.ac long ago



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@51288 65c4cc65-6c06-0410-ace0-fbb531ad65f3

configure.ac

@@ -28,7 +28,7 @@ AC_COPYRIGHT("Asterisk")
 AC_REVISION($Revision$)
 
 AC_GNU_SOURCE
-AC_USE_SYSTEM_EXTENSIONS
+AC_USE_SYSTEM_EXTENSIONS	# note- does not work on FreeBSD
 
 case "${host_os}" in
      freebsd*)
@@ -36,6 +36,7 @@ case "${host_os}" in
      CPPFLAGS=-I/usr/local/include
      LDFLAGS=-L/usr/local/lib
      ;;
+
      *)
      ac_default_prefix=/usr
      if test ${sysconfdir} = '${prefix}/etc'; then
@@ -127,7 +128,7 @@ AC_PROG_CPP
 AC_PROG_CXXCPP
 # This macro is just copied into our local acinclude.m4 from libtool.m4 so that
 # the developers regenerating the configure script don't have to install libtool.
-AST_PROG_LD
+AST_PROG_LD	# note, does not work on FreeBSD
 AC_PROG_AWK
 AC_PROG_INSTALL
 AC_PROG_LN_S