To cross build tcl package, following patch improve
situation.

In general configure scheme, we can override and skip
test with configure cache file.  It is very useful for
cross build, where we the test of AC_TRY_RUN cannot
execute (because of build != host).

In tcl's unix configure, there are three check, where this
override doesn't work.

I think that any AC_TRY_RUN should be enclosed with
AC_CACHE_VAL for cross build.