configure.ac: replace deprecated aliases

configure.ac: replace deprecated aliases

See https://www.gnu.org/software/libtool/manual/html_node/LT_005fINIT.html

    configure.ac:25: warning: The macro `AM_ENABLE_STATIC' is obsolete.
    configure.ac:25: You should run autoupdate.
    m4/ltoptions.m4:259: AM_ENABLE_STATIC is expanded from...
    configure.ac:25: the top level
    configure.ac:26: warning: The macro `AM_ENABLE_SHARED' is obsolete.
    configure.ac:26: You should run autoupdate.
    m4/ltoptions.m4:205: AM_ENABLE_SHARED is expanded from...
    configure.ac:26: the top level