[LTO merge] Merge status and latest patch

[Diego Novillo <dnovillo at google dot com>]

These are the issues that need to be addressed before the final
merge:

1- C++ mangling.  I am implementing the idea of discarding
   TEMPLATE_DECLs.  My latest attempt at the langhook didn't
   work.

2- Complete usage documentation.  Joseph wants more user-level
   information before agreeing to the merge.  I will add that
   today.

3- Portability issues with __attribute__ ((visibility ("hidden")))
   and mmap.  This affects sparc-sun-solaris2.10 and
   i686-mingw32. http://gcc.gnu.org/ml/gcc-patches/2009-09/msg02157.html

4- Enable LTO from common.opt instead of each individual FE.
   This may break FEs that are not prepared for it, so we will
   defer this until after the merge.

Anything else?  I would appreciate some help for #3, as I would
like to finalize the merge this week.  If not, I'll get to it
sometime next week.

Attached is the latest unified patch against rev 152279.


Thanks.  Diego.

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