Add dlwrap.c to binutils to simulate dlopen/dlsym for gold plugin

This allows us to link the gold-plugin in directly instead of using it as a DSO.

This is part of change:
http://codereview.chromium.org/8698014/

BUG= http://code.google.com/p/nativeclient/issues/detail?id=2286

[robertm, 2011-11-28 17:50:26]

I would have preferred to make the shared libs work on windows
until Ivan has a pure llvm replacement (i.e. no binutils).

But as a temporary work around it might be OK.
what is the maintenance burden of this? I do not see any localmods.
Do we expect binutils to be stable until say the end of the year?

[pdox, 2011-11-28 18:10:04]

I tried to keep everything well isolated.

The biggest maintenance will be the configure/Makefile's, which I've modified a
couple of lines to build dlwrap and include it in the link. (along with
gold-plugin-static.o).

While we're using gold + gold plugin, this is a permanent solution. There is
basically no performance hit here, but this is a lot less buggy on
Windows/Cygwin. Even if we fix the Windows bot, other people using our windows
toolchain would likely run into DSO loading problems.

[krasin, 2011-11-28 18:57:48]

Is any urgency with addressing this issue (Windows bot is broken)? Why just not
wait until we have a pure bitcode linker and this problem will go away w/o any
additional cost?

[sehr (please use chromium), 2012-02-15 19:47:57]

OK, I'm accepting the argument that this is a temporary hack until we can get
bitcode linking going.  We need a windows toolchain for the dogfood, so let's go
ahead.

http://codereview.chromium.org/8713008/diff/5001/binutils-2.20/dlwrap.c
File binutils-2.20/dlwrap.c (right):

http://codereview.chromium.org/8713008/diff/5001/binutils-2.20/dlwrap.c#newcode3
binutils-2.20/dlwrap.c:3: 
Please add explicitly a comment that this is a hack to get a windows pnacl
toolchain working.

[pdox, 2012-02-17 22:48:14]

This CL has been greatly simplified. PTAL.

[sehr (please use chromium), 2012-02-17 23:19:01]

On 2012/02/17 22:48:14, pdox wrote:
> This CL has been greatly simplified. PTAL.

LGTM.