Proposal to remove std stream and file chain info from reent struct

[Jeff Johnston]

In light of the following post:

http://sourceware.org/ml/newlib/2010/msg00376.html

I am proposing to remove the std streams from the reentrancy structure 
and have one global set.  As well, the glue chain can also be removed 
since we would always be using the one chain.  I am proposing a new 
global structure which would house the std streams and the glue chain.

The current std stream situation appears to be mostly historical.  I'm 
not sure anyone actually depends on there being std streams per thread. 
POSIX thread and I/O behaviour certainly wasn't ever considered in the 
initial implementation.

There are obvious benefits to doing this.  The reentrancy struct gets 
smaller.  The scenario problem, described in the newlib posted link 
above, goes away.  In addition, the code gets simplified as some 
reentrant versions of functions are not needed.

I am proposing this here first in case any platform has a dependency on 
the current behaviour or there are some gotchas I haven't thought of.

If there are no fundamental objections, I will make the changes and post 
a patch here for review/comments.

-- Jeff J.