create mode 100644 src/Sema/arith.zig delete mode 100644 test/cases/compile_errors/add_on_undefined_value.zig delete mode 100644 test/cases/compile_errors/div_on_undefined_value.zig delete mode 100644 test/cases/compile_errors/mult_on_undefined_value.zig delete mode 100644 test/cases/compile_errors/mult_sat_on_undefined_value.zig delete mode 100644 test/cases/compile_errors/mult_wrap_on_undefined_value.zig delete mode 100644 test/cases/compile_errors/sub_on_undefined_value.zig create mode 100644 test/cases/compile_errors/undef_arith_is_illegal.zig create mode 100644 test/cases/compile_errors/undef_arith_returns_undef.zig