* configure.ac (emacs_config_options): Record some env vars.

configure.ac

@@ -23,9 +23,21 @@ dnl  along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
 
 AC_PREREQ(2.65)
 AC_INIT(emacs, 24.3.50)
+
 dnl This is the documented way to record the args passed to configure,
 dnl rather than $ac_configure_args.
 emacs_config_options="$@"
+## Add some environment variables, if they were passed via the environment
+## rather than on the command-line.
+for var in CFLAGS CPPFLAGS LDFLAGS; do
+    case "$emacs_config_options" in
+      *$var=*) continue ;;
+    esac
+    eval val="\$${var}"
+    test x"$val" = x && continue
+    emacs_config_options="${emacs_config_options}${emacs_config_options:+ }$var=$val"
+done
+
 AC_CONFIG_HEADER(src/config.h:src/config.in)
 AC_CONFIG_SRCDIR(src/lisp.h)
 AC_CONFIG_AUX_DIR(build-aux)