Correct ix86_rtx_cost for multi-word multiplication.

Correct ix86_rtx_cost for multi-word multiplication.

This is the i386 backend specific piece of my revised patch for
PR middle-end/98865, where Richard Biener has suggested that I perform
the desired transformation during RTL expansion where the backend can
control whether it is profitable to convert a multiplication into a
bit-wise AND and a negation.  This works well for x86_64, but alas
exposes a latent bug with -m32, where a DImode multiplication incorrectly
appears to be cheaper than negdi2+anddi3(!?).  The fix to ix86_rtx_costs
is to report that a DImode (multi-word) multiplication actually requires
three SImode multiplications and two SImode additions.  This also corrects
the cost of TImode multiplication on TARGET_64BIT.

2022-05-18  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	* config/i386/i386.cc (ix86_rtx_costs) [MULT]: When mode size
	is wider than word_mode, a multiplication costs three word_mode
	multiplications and two word_mode additions.