re PR rtl-optimization/87761 ([MIPS] New FAIL: gcc.target/mips/fix-r4000-10.c   -O1 start with r265398)

	PR rtl-optimization/87761
	* config/mips/mips.md: Add new combiner pattern to recognize
	a bitfield extraction using (ashiftrt (truncate (ashift (...)))).

From-SVN: r269123