some header bugs

[DJ Delorie]

While building some internal Red Hat stuff, I noticed the following:

In /usr/include/termcap.h, some variables are declared "extern" but
there's no provision for marking them as dllimport when you link
against the dll version of the termcap library, which is the default.

In /usr/include/sys/unistd.h, setdtablesize() is defined as returning
void, but bash/builtins/ulimit.def wants it to return an int (an
error code if any).

And just to beat Chris to it, "Patches welcome."  :-)