libstdc++: Avoid intercepting exception in ostream::write

libstdc++: Avoid intercepting exception in ostream::write

Currently if ostream::write fails and sets badbit and that causes an
exception, we will catch the exception, set badbit again, and rethrow
the exception.

This change delays setting badbit until after the try-catch block, so
that if it causes an exception we don't need to catch and rethrow it.

This removes the last remaining use of _M_write, so it can be made
private (or removed entirely for versioned namespace builds, where ABI
compatibility is not required). All other uses of _M_write were replaced
by calls to __ostream_insert, so make _M_write use that too.

libstdc++-v3/ChangeLog:

	* include/bits/ostream.tcc (basic_ostream::write): Call sputn
	directly instead of using _M_write. Do setstate(__err) all
	outside the try-catch block.
	* include/std/ostream (basic_ostream::_M_write): Declare
	private. Use __ostream_insert. Do not define for the versioned
	namespace.