[build] Move unwinder to toplevel libgcc

[Joseph S. Myers]

On Mon, 20 Jun 2011, Rainer Orth wrote:

> Certainly: your wiki entry gives a good overview.  For the moment, I'll
> probably concentrate on the build side of things, though.  I may attack
> gthr* stuff and fp-bit.[ch] next, both of which I can at least partially
> test on my targets.

fp-bit.[ch] has the interesting issue of FLOAT_BIT_ORDER_MISMATCH and 
FLOAT_WORD_ORDER_MISMATCH being defined by makefile rules when it ought to 
be possible to deduce that information from macros predefined by the 
compiler.  (See what I said in 
<http://gcc.gnu.org/ml/gcc-patches/2010-11/msg02262.html> about the 
meanings of those macros.)

dfp-bit.* and fixed-bit.* can probably move along with fp-bit.* (or 
before, or after), and I don't think there are any complicated issues 
around those files.

-- 
Joseph S. Myers
joseph@codesourcery.com