MSP430: Define NO_FUNCTION_CSE

MSP430: Define NO_FUNCTION_CSE

Calling a constant function address costs the same number of clock
cycles as calling an address stored in a register. However, in terms of
instruction length, calling a constant address is more expensive.

Set NO_FUNCTION_CSE to true, only when optimizing for speed.

gcc/ChangeLog:

	* config/msp430/msp430.h (NO_FUNCTION_CSE): Set to true at -O2 and
	above.