[tlbuild] build failure: libs/zziplib/zziplib-0.13.58/zzip/stat.c needs #include <strings.h> for strcasecmp

[Karl Berry]

    #ifndef HAVE_STRCASECMP
    #include <strings.h>
    #endif

I fear pulling in incompatible declarations.  But it seems there is no
reasonable alternative, so let's try it.