LoongArch: Add tests for ASX vector xvadd/xvadda/xvaddi/xvaddwev/ xvaddwodxvsadd instructions.
gcc/testsuite/ChangeLog:
* gcc.target/loongarch/vector/lasx/lasx-xvadd.c: New test.
* gcc.target/loongarch/vector/lasx/lasx-xvadda.c: New test.
* gcc.target/loongarch/vector/lasx/lasx-xvaddi.c: New test.
* gcc.target/loongarch/vector/lasx/lasx-xvaddwev-1.c: New test.
* gcc.target/loongarch/vector/lasx/lasx-xvaddwev-2.c: New test.
* gcc.target/loongarch/vector/lasx/lasx-xvaddwev-3.c: New test.
* gcc.target/loongarch/vector/lasx/lasx-xvaddwod-1.c: New test.
* gcc.target/loongarch/vector/lasx/lasx-xvaddwod-2.c: New test.
* gcc.target/loongarch/vector/lasx/lasx-xvaddwod-3.c: New test.
* gcc.target/loongarch/vector/lasx/lasx-xvsadd-1.c: New test.
* gcc.target/loongarch/vector/lasx/lasx-xvsadd-2.c: New test.