[patch] Define new std::ios_base::failure with abi_tag("cxx11")

[Jonathan Wakely]

This adds system_error support to iostreams, including the required
base class changes to std::ios_base::failure. The abi_tag is used to
make it a distinct type.  This changes the type of I/O exceptions
thrown by the library but exceptions are very rarely used with
iostreams.

Tested powerpc64-linux and x86_64-linux
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