[Windows toolchain] link failures from command prompt

I just filed a bug report (http://llvm.org/bugs/show_bug.cgi?id=17428)
against LLVM-3.4.r191323-win32.exe. Here is the rationale for considering
failure to link under the "Developer Command Prompt for VS2012" a bug:

Boost developers and test runners, and probably lots of other folks too, run
their automated tests from the command prompt rather than via the IDE. So it
is a showstopper for these folks if the clang windows toolchain doesn't work
from the command prompt.

In my little hello.cpp test the clang++ compile was clean, but the link had
unresolved externals like "hello-111ee3.o : error LNK2019: unresolved
external symbol __ZSt4cout referenced in function _main".

That's particularly frustrating since it is so close to working!

Once the command prompt is working, I'll submit a patch to
http://llvm.org/builds/ explaining how to use it.

Thanks,

--Beman

I know,Visual Studio Use Microsoft C++ ABI,But Clang Use Itanium ABI ,They are not the same as Name mangling。

------------------ Original ------------------

I know,Visual Studio Use Microsoft C++ ABI,But Clang Use Itanium ABI ,They
are not the same as Name mangling。

Clang does support a lot of the MS C++ ABI, but the 'clang++' driver
defaults to using the Itanium ABI. See the comments on the bug for more
information.