target/i386: Fix calculation of LOCK NEG eflags

After:

        lock negl -0x14(%rbp)
        pushf
        pop    %rax

%rax will contain the wrong value because the "lock neg" calculates the
wrong eflags.  Simple test:

        #include <assert.h>

        int main()
        {
          __volatile__ unsigned test = 0x2363a;
          __volatile__ char cond = 0;
          asm(
              "lock negl %0 \n\t"
              "sets %1"
              : "=m"(test), "=r"(cond));
          assert(cond & 1);
          return 0;
        }

Reported-by: Jinyang Shen <shenjinyang@loongson.cn>
Co-Developed-by: Xuehai Chen <chenxuehai@loongson.cn>
Signed-off-by: Xuehai Chen <chenxuehai@loongson.cn>
Signed-off-by: Qi Hu <huqi@loongson.cn>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

target/i386/tcg/translate.c

@@ -3300,7 +3300,7 @@ static bool disas_insn(DisasContext *s, CPUState *cpu)
 
                 tcg_temp_free(t2);
                 tcg_temp_free(a0);
-                tcg_gen_mov_tl(s->T0, t0);
+                tcg_gen_neg_tl(s->T0, t0);
                 tcg_temp_free(t0);
             } else {
                 tcg_gen_neg_tl(s->T0, s->T0);