The relevant parts of the .c code appear to be in win32.c

char *win32_get_sitelib(const char *pl)
{
    return win32_get_xlib(pl, "sitelib", "site");
}


static char *win32_get_xlib(const char *pl, const char *xlib, const ch
+ar *libname)
{

 ....

    sprintf(pathstr, "%s/lib", libname);
    (void)get_emd_part(&sv2, pathstr, ARCHNAME, "bin", pl, Nullch);

    /* JJ -- get_emd_part strips 'bin' if possible from 
             the path to the .dll (found in get_emd_part
             by calling set_w32_module_name(); ) and then
             adds 'site/lib' to that path
     */

 ...
}
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