msp430.c (is_wakeup_func): New function.

	* config/msp430/msp430.c (is_wakeup_func): New function.  Returns
	true if the current function has the wakeup attribute.
	(msp430_start_function): Note if the function has the wakeup
	attribute.
	(msp430_attribute_table): Add wakeup attribute.
	(msp430_expand_epilogue): Add support for wakeup functions.
	* config/msp430/msp430.md (disable_interrupts): Emit a NOP after
	the DINT instruction.
	* doc/extend.texi: Document the wakeup attribute.

From-SVN: r205958