* 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.