libsanitizer: enable libubsan and libasan for loongarch64-*-linux*

The LoongArch support for libubsan and libasan has been added in:

- https://reviews.llvm.org/D129371
- https://reviews.llvm.org/D129418

and we've merged them in r13-2269.  It's time to enable them.

No unexpected failures in GCC asan.exp and ubsan.exp tests.

libsanitizer/ChangeLog:

	* configure.tgt: Allow loongarch64-*-linux*.

libsanitizer/configure.tgt

@@ -72,6 +72,8 @@ case "${target}" in
 	;;
   riscv64-*-linux*)
 	;;
+  loongarch64-*-linux*)
+	;;
   *)
 	UNSUPPORTED=1
 	;;