dnldnl Allow the user to enable or disable the use of a function. If thednl option is not specified, the function is auto-detected.AC_DEFUN([MPD_OPTIONAL_FUNC], [ AC_ARG_ENABLE([$1], AS_HELP_STRING([--enable-$1],
[use the function "$1" (default: auto)]), [test xenable_$1 = xyes && AC_DEFINE([$3], 1, [Define to use $1])], [AC_CHECK_FUNC([$2], [AC_DEFINE([$3], 1, [Define to use $1])],)])