i386: Use TImode for BLKmode values in 2 integer registers

i386: Use TImode for BLKmode values in 2 integer registers

When passing and returning BLKmode values in 2 integer registers, use
1 TImode register instead of 2 DImode registers. Otherwise, V1TImode
may be used to move and store such BLKmode values, which prevent RTL
optimizations.

gcc/

	PR target/87370
	* config/i386/i386.c (construct_container): Use TImode for
	BLKmode values in 2 integer registers.

gcc/testsuite/

	PR target/87370
	* gcc.target/i386/pr87370.c: New test.

From-SVN: r264716