PNaCl documentation: explain how PNaCl can build with a different C++ standard library, and how to …

native_client_sdk/src/doc/devguide/devcycle/building.rst

 .. _devcycle-building:
 
 ########
 Building
 ########
 
 .. contents:: Table Of Contents
   :local:
   :backlinks: none
   :depth: 2
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 C libraries
 -----------
 
 The Native Client SDK comes with two C libraries: `newlib
 <http://sourceware.org/newlib/>`_ and `glibc
 <http://www.gnu.org/software/libc/>`_. See :doc:`Dynamic Linking & Loading with
 glibc <dynamic-loading>` for information about these libraries, including
 factors to help you decide which to use.
 
+C++ libraries
+-------------
+
+Native Client can only use GCC's `libstdc++
+<http://gcc.gnu.org/libstdc++>`_, whereas Portable Native Client can use
+either `libstdc++ <http://gcc.gnu.org/libstdc++>`_ (the current default)
+and also has preliminary support for LLVM's `libc++
+<http://libcxx.llvm.org/>`_. The ``-stdlib=[libstdc++|libc++]`` command
+line argument can be used to choose which standard library to use.
+
+C++11 library support is only complete in libc++ but other non-library
+language features should work regardless of which standard library is
+used. The ``-std=[c++98|c++11]`` command line argument can be used to
+indicate which C++ language standard to use.
+
 SDK toolchains
 --------------
 
 The Native Client SDK includes multiple toolchains, differentiated by target
 architectures and C libraries. The toolchains are located in directories named
 ``toolchain/<platform>_<architecture>_<library>``, where:
 
 * *<platform>* is the platform of your development machine (win, mac, or linux)
 * *<architecture>* is your target architecture (x86 or arm)
 * *<library>* is the C library you are compiling with (newlib or glibc)
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   If your code uses mkdir or other file system calls, you might find nacl-mounts
   useful. Nacl-mounts essentially does option (3) for you: It lets your code
   use POSIX-like file system calls, and implements the calls using various
   technologies (e.g., App Engine or an in-memory filesystem).
 
 Can't find libraries containing necessary symbols
   Here is one way to find the appropriate library for a given symbol::
 
     nm -o toolchain/<platform>_x86_<library>/x86_64-nacl/lib64/*.a | grep <MySymbolName>