#!/bin/sh
while test -n "$1"; do
  case "$1" in
  (--*=*)
    val=${1#--}
    name=${val%%=*}
    val=${val#*=}
    export "$(printf "%s\n" "$name"|tr '[:lower:]-' '[:upper:]_')=$val"
    ;;
  esac
  shift
done

(
  # Variables that the makefile uses and that are meant to be configurable
  awk '/ \?=/ {print($1)}' Makefile
  # Variables that GNU Make uses for the implicit rules
  cat <<EOF
CC
CPPFLAGS
CFLAGS
LDFLAGS
LOADLIBES
LDLIBS
EOF
)|sort -u|while read varname; do
  eval "test -n \"\${$varname+x}\" && echo \${varname}=\${$varname}"
done|tee config.mak