LoongArch: Add tests for SX vector vmax/vmaxi/vmin/vmini instructions.
gcc/testsuite/ChangeLog:
* gcc.target/loongarch/vector/lsx/lsx-vmax-1.c: New test.
* gcc.target/loongarch/vector/lsx/lsx-vmax-2.c: New test.
* gcc.target/loongarch/vector/lsx/lsx-vmaxi-1.c: New test.
* gcc.target/loongarch/vector/lsx/lsx-vmaxi-2.c: New test.
* gcc.target/loongarch/vector/lsx/lsx-vmin-1.c: New test.
* gcc.target/loongarch/vector/lsx/lsx-vmin-2.c: New test.
* gcc.target/loongarch/vector/lsx/lsx-vmini-1.c: New test.
* gcc.target/loongarch/vector/lsx/lsx-vmini-2.c: New test.