Harmonize generic stdio-lock support with nptl

	This fixes build when _IO_funlockfile is a macro, fixes build where
	_IO_acquire_lock_clear_flags2 is used, and fixes unlocking on unexpected
	stack unwind.

	* sysdeps/generic/stdio-lock.h [__EXCEPTIONS] (_IO_acquire_lock,
	_IO_release_lock ): Use cleanup attribute on new
	_IO_acquire_lock_file variable instead of assuming that
	_IO_release_lock will be called.
	[!__EXCEPTIONS] (_IO_acquire_lock): Define to non-existing
	_IO_acquire_lock_needs_exceptions_enabled.
	(_IO_acquire_lock_clear_flags2): New macro.