LoongArch: Add tests for ASX vector xvhadd/xvhaddw/xvmaddwev/xvmaddwod instructions.
gcc/testsuite/ChangeLog:
* gcc.target/loongarch/vector/lasx/lasx-xvhaddw-1.c: New test.
* gcc.target/loongarch/vector/lasx/lasx-xvhaddw-2.c: New test.
* gcc.target/loongarch/vector/lasx/lasx-xvmadd.c: New test.
* gcc.target/loongarch/vector/lasx/lasx-xvmaddwev-1.c: New test.
* gcc.target/loongarch/vector/lasx/lasx-xvmaddwev-2.c: New test.
* gcc.target/loongarch/vector/lasx/lasx-xvmaddwev-3.c: New test.
* gcc.target/loongarch/vector/lasx/lasx-xvmaddwod-1.c: New test.
* gcc.target/loongarch/vector/lasx/lasx-xvmaddwod-2.c: New test.
* gcc.target/loongarch/vector/lasx/lasx-xvmaddwod-3.c: New test.