MSP430: Add 64-bit hardware multiply support

MSP430: Add 64-bit hardware multiply support

Hardware multipliers that support widening 32-bit multiplication can
be used to perform a 64-bit * 64-bit multiplication more efficiently
than a software implementation.

The following equation is used to perform 64-bit multiplication for
devices with "32bit" or "f5series" hardware multiply versions:

  64bit_result = (low32_op0 * lop32_op1)
    + ((low32_op0 * high32_op1) << 32)
       + ((high32_op0 * low32_op1) << 32)

libgcc/ChangeLog:

	* config/msp430/lib2hw_mul.S (mult64_hw): New.
	(if MUL_32): Use mult64_hw for __muldi3.
	(if MUL_F5): Use mult64_hw for __muldi3.
	* config/msp430/lib2mul.c (__muldi3): New.
	* config/msp430/t-msp430 (LIB2FUNCS_EXCLUDE): Define.