Comment # 6 on bug 1119646 from Dr. Werner Fink

From ncurses-6.1/INSTALL

    --enable-opaque-curses
    --enable-opaque-form
    --enable-opaque-menu
    --enable-opaque-panel
        Define symbol in curses.h which controls whether some library
        structures are treated as "opaque".  The --enable-opaque-curses option
        is overridden by the --enable-reentrant option.

... --enable-reentrant is set

    --enable-reentrant
        Compile configuration which improves reentrant use of the library by
        reducing global and static variables.  This option is also set if
        --with-pthread is used.

        Enabling this option adds a "t" to the library names, except for the
        special case when --enable-weak-symbols is also used.

... and also --enable-weak-symbols ... there is no "t" added to the library
names