(cmpM_cc): Allow first operand to be a MEM.

Don't allow both operands to be MEM.
(float addM3,subM3,divM3,mulM3 recognizers): Don't allow either operand
to be a constant.
(all float patterns, FLOAT_EXTEND operands): Don't allow GENERAL_REGS
for float_extended operand.
(all float patterns, FLOAT operands): Change constraints to get better
register classification.
(fix_truncMN2 patterns): Likewise.
(floatMN2 patterns): Likewise.

From-SVN: r3296