Initial draft of PNaCl bitcode files.

native_client_sdk/src/doc/reference/pnacl-c-cpp-language-support.rst

 ============================
 PNaCl C/C++ Language Support
 ============================
 
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 Source language support
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 Auto-vectorization is currently not enabled for Portable Native Client,
 but will be in a future release.
 
 Undefined Behavior
 ==================
 
 The C and C++ languages expose some undefined behavior which is
 discussed in :ref:`PNaCl Undefined Behavior <undefined_behavior>`.
 
+.. _c_cpp_floating_point:
+
 Floating-Point
 ==============
 
 PNaCl exposes 32-bit and 64-bit floating point operations which are
 mostly IEEE-754 compliant. There are a few caveats:
 
 * Some :ref:`floating-point behavior is currently left as undefined
   <undefined_behavior_fp>`.
 * The default rounding mode is round-to-nearest and other rounding modes
   are currently not usable, which isn't IEEE-754 compliant. PNaCl could
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   A similar feature is **thread suspension**: The ability to
   asynchronously suspend and resume a thread and inspect or modify its
   execution state (such as register state).
 
   Neither PNaCl nor NaCl currently support asynchronous interruption
   or suspension of threads.
 
 If PNaCl were to support either of these, the interaction of
 ``volatile`` and atomics with same-thread signal handling would need
 to be carefully detailed.