Clean up Makefile "warning" clutter when makeopts doesn't exist.

Review: https://reviewboard.asterisk.org/r/2304


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@384989 65c4cc65-6c06-0410-ace0-fbb531ad65f3

build_tools/make_linker_version_script

@@ -1,5 +1,6 @@
 #!/bin/sh
 
+AWK=${AWK:-awk}
+
 test -f ${1}.exports.in && ${AWK} "{sub(\"LINKER_SYMBOL_PREFIX\", \"${2}\"); print;}" ${1}.exports.in > ${1}.exports && exit 0
 test -f ${1}.exports.in || rm -f ${1}.exports && cp ${3}/default.exports ${1}.exports && exit 0
-