gh-22: Amend float detection patch to use private Autoconf variables

Author: erlend-aasland

autoconf/ax_c_float_words_bigendian.diff

@@ -82,11 +82,11 @@ index 216b90d8..52036844 100644
  ]])], [
 
 -if grep noonsees conftest.$ac_objext >/dev/null ; then
-+if grep noonsees conftest$EXEEXT >/dev/null ; then
++if grep noonsees conftest$ac_exeext >/dev/null ; then
    ax_cv_c_float_words_bigendian=yes
  fi
 -if grep seesnoon conftest.$ac_objext >/dev/null ; then
-+if grep seesnoon conftest$EXEEXT >/dev/null ; then
++if grep seesnoon conftest$ac_exeext >/dev/null ; then
    if test "$ax_cv_c_float_words_bigendian" = unknown; then
      ax_cv_c_float_words_bigendian=no
    else