New reg note REG_CFA_NORESTORE

New reg note REG_CFA_NORESTORE

This patch introduces a new reg note which can be used to tell the CFI
verification in dwarf2cfi that a register is stored without intending
to restore from it.

This is useful when storing e.g. register contents to the stack and
generate CFI for it although the register is not really supposed to be
restored.

gcc/ChangeLog:

	* dwarf2cfi.cc (dwarf2out_frame_debug_cfa_restore): Add
	EMIT_CFI parameter.
	(dwarf2out_frame_debug): Add case for REG_CFA_NORESTORE.
	* reg-notes.def (REG_CFA_NOTE): New reg note definition.