[test] Disable the -Wself-move warning that triggers on exactly what is being tested (NFC)

/Users/jiefu/llvm-project/llvm/unittests/Option/OptionParsingTest.cpp:251:6: error: explicitly moving variable of type 'InputArgList' to itself [-Werror,-Wself-move]
  AL = std::move(AL);
  ~~ ^           ~~
1 error generated.