boost_program_options and autoconf on non-amd64 platforms

["Maarten L. Hekkelman" <maarten@hekkelman.com>]

    I noticed my recently submitted package libzeep does not build on
    architectures other than amd64. The configure script dies since it
    cannot find the library to link against.
    
    When I tried this on a Debian buster install on an armel system, I
    had the same problem. One way to work around this is defining a
    variable in advance, like this:

if test "x$ax_boost_user_program_options_lib" = "x"; then

ax_boost_user_program_options_lib=boost_program_options

fi

before the statement:

AX_BOOST_PROGRAM_OPTIONS in the configure.as script.

    Is this a known problem? The variable AX_BOOST_PROGRAM_OPTIONS
    refers to a m4 macro that originates from the autoconf-archive
    package and that package hasn't changed recently as far as I can
    see. So the reason for failure must lie elsewhere.
    
    I can try to figure out what really goes wrong, but since that might
    involve quite a bit of work, I'd rather do that only when really
    necessary.
    
    regards, -maarten